Actually, it seems like a sort of consensus is emerging that “data are” is more common, if not actually preferred, in scientific contexts, and “data is” is more common in business contexts. Certainly, most of the time I use the word “data,” it’s in a business sense. I can’t see us ever using the word “datum” at work – but we do use “data point” rather a lot.
Also, I should say, in reference to my OP, that “quaintness” doesn’t seem to come into play here. I’ll just keep the quaintness award for myself, thanks, in recognition of my other quaint qualities (like excessive use of the letter “q,” apparently).
Yep, it’s common. such as this link: Aquarium Decorations & Decor for Tanks | That Fish Place
You’re a Brit, methinks. I was too, back in the days of studying Latin. But now I’m smart enough to drive on the right side of the road, and spell honor the honorable way 
Googlefight: “data is” vs. “data are.” The former beats the latter, 225 million to 101 million.
Call me a stodgy curmudgeon, but I consider data plural, along with media and criteria. However, rather than calling attention to it by attaching a verb to “data” as the subject, I’ll usually rework the sentence so “data” is the object or indirect object, making its singular/plural value irrelevant.
As in, rather than “the data aren’t guaranteed to be clean,” I’ll say, “let’s check the data for cleanliness” or something.
I’ve given up on agenda, though.
Finally, someone with no agendum!
Does anyone use data as singular?
Can one collect a data?
If I tried to misuse data as singular, my boss would be annoyed at my careless mistake. You can collect a data point, reference a datum, and show these data.
To me and the people I work with (all technical types) it isn’t a question.
No, but one may collect some data. I don’t think it’s really ever treated like a singular noun, but rather a collective noun like “sugar”. Most people have no use for “a sugar”, but “sugar is” is a perfectly correct construction.
I try to use datum and criterion in conversation whenever I can. It seems to befuddle and annoy. They can’t quite bring themselves to call me a pedantic twat, because they just know it’s correct; but for some reason it grates on the nerves of some folks.
I will henceforth go looking for any and all excuses to gratutitously pepper conversation with “agendum”, which I had, in my negligence, forgotten.
Any other defunct singulars I can irritate people with?
No, but you can try to figure out the correct plural of “omnibus”.
Actually it’s already plural - dative or ablative plural of “omnis”, and in context meaning something like “for everyone”
A higher purpose in life, my good man, I simply cannot conceive. 
Is not what we’re seeing a hold-over from Classical Greek, where neuter plurals take a singular verb?
Ah, but you missed my point. I’m not fighting the battle at all. If you say “The data shows…”, I will neither ridicule you nor become annoyed. I will continue to say “The data show…”, and I will only react if somebody corrects me when I use data as plural and datum as singular.
It’s a “live and let live” approach. I’m realist enough to know that when most of the world misuses or mispronounces a word, it becomes “correct” after a while. So many people pronounce “err” as “air” that’s it not worth correcting them. The error has become the norm. I won’t fight that losing battle, but I won’t start saying it wrong myself, either.
Ah, a man after my own heart! If you don’t already have it, I would highly recommend The Superior Person’s Book of Words, which has befuddlement and annoyance of one’s listeners as its major objective.
Ehhhxcellent!
Off to Amazon!
Fascinating. Along those lines: In Arabic, all nouns denoting nonrational entities take the feminine singular verb when they’re plural. The only time plural verbs are used is for rational beings.*
*defined as humans, jinn, angels, and God; all other nouns are nonrational.
taqifu al-mar’ah ‘The woman stands’. Feminine singular.
taqifna al-nisa’ ‘The women stand’. Feminine plural.
yaqifu al-rajul ‘The man stands’. Masculine singular.
yaqifuna al-rijal ‘The men stand’. Masculine plural.
So far this is the normal way we’d expect plurals to function with verbs. But:
yaqifu al-bayt ‘The house stands’. Masculine singular.
taqifu al-buyut ‘The houses stand’. Feminine singular.
tara ‘ayni ‘My eye sees’. Feminine singular.
tara ‘uyunuhum ‘Their eyes see’. It’s still feminine singular.
Collective nouns take the masculine singular. Count nouns belonging to said collectives take the feminine singular (even when they’re plural).
yasqutu tuffah ‘Apples fall’. Masculine singular.
tasqutu tuffahah ‘An apple falls’. Feminine singular.
(The letter t- marks the feminine gender. The -h at the end of tuffahah is actually a feminine gender marker -t in disguise, which agrees with the t- in the verb conjugation. It only looks like an h in the pause form. It changes back to t when something follows it, e.g. tuffahati ‘my apple’. Did I mention that Arabic grammar is very complex? Is anyone still with me?)
It gets stranger: Plurals of masculine nouns take the feminine singular.
qara’a kitab ‘A book was read’. Masculine singular.
qara’at kutub ‘Books were read’. Feminine singular.
Like I often say, “Go figure.”
I have wondered if this anomalous gender/number behavior in Arabic can be connected with an explanation I read on how gender first developed in Proto-Indo-European from active and stative noun categories. My idea went like this:
I found it interesting because of a similar development in Arabic. The broken plural of an Arabic nonrational masculine noun agrees with the feminine singular adjective and with the feminine singular verb.
For example: in
dahaka al-kalb al-saghîr ‘The little dog laughed’. (Masculine singular in both verb and adjective agreement)
dahakat al-kilâb al-saghîrah ‘The little dogs laughed’. (Feminine singular)
the broken plural kilâb (dogs) makes the verb take the feminine ending -t and the adjective the feminine ending -ah ~ -at-.
As for the active/stative contrast, Arabic distinguishes not between animate
and inanimate, but between “rational” (‘âqil) and “irrational” beings – the
former includes humans, angels, and jinn; the latter includes animals as well
as inanimate things.
Masculine rational nouns take a sound or broken plural agreeing with masculine plural adjectives and verbs. Likewise, sound plurals of feminine rational nouns (ending in -ât) agree with feminine plural adjectives and verbs. But plurals of feminine irrational nouns agree with the feminine singular!
For example,
rajul sâlih (a righteous man), rijâl sâlihûn (righteous men);
sayyidah muslimah (a Muslim lady), sayyidât muslimât (Muslim ladies) –
but
‘ayn fawwârah (a bubbling spring), ‘uyûn fawwârah (bubbling springs).
Another curious use of number in Arabic is the way plants, fruits, and stones
are designated by a masculine collective noun, while the singular (noun of
unity) takes the feminine ending. For example:
shajar (trees), shajarah (a tree);
sakhr (rocks), sakhrah (a rock). Qubbat al-Sakhrah is the Dome of the Rock.
P.S. Quartz, this sentence is in the above referenced article: “It is also why the Greek neuter plural took a singular verb.”
The distinction is informative, and language changes too quickly. Our history and cultural origins would be so much easier to know and understand if we would be more stringent in our standards for grammar, usage, &c. Og knows, I make plenty of mistakes, but at least I try. Well, I try to try, anyway. Frankly, I don’t understand why people would want the great authors of today to be as incomprehensible to future generations as Shakespear and Chaucer are to us. We’ve invented the technologies of spelling and grammar, why not use them? One might as well crap in the yard…
“What are you doing? You’re crapping the yard!”
“Well, sanitation standards change over time. Get over it; stop being so quaint.”
(It’s fairly recently that I’ve come to this view, by the way, because I’ve seen how badly people are harmed by poor writing and speaking. I cannot eschew conservative language standards because I’m finding it to be unethical.)
Me too.
Sorry, I forgot to put it in the passive voice. Should have typed quri’a. See how Arabic inflects grammatically by changing the vowels inside a word while keeping the consonantal root in place. The neatness of this system allows Arabic to develop great richness and precision despite the gnarly complexity, which explains why so many people are able to study it and get a lot out of it despite the difficulty.
As for keeping up those high standards of English, I don’t think there’s any cause for alarm. The standard written English known to all properly educated English-speaking people is always changing, of course, but not changing at such a rate that one generation can’t understand the next. Hal westu, Maria, þu eart geofe ful.
Makes sense then why academic journals insist on it then. 
I say datum/data, criterion/criteria aquarium/aquaria and agendum/agenda all the time. I know it annoys people, and I think that is part of the reason I insist on using it…and because it is correct.
I wish I could say I have some high-minded reason for “holding out”, but I do it mostly for the negative attention.