No problem … as long as we are discussing only English, we can mutually understand terms like “long” and “short” as they were taught to us in grade school.
To me, it’s preferable to say that the trigraph IGH now represents a “long I” sound rather than to say that it’s the GH that makes an otherwise short I into a long I.
That’s fine – but if you ask about the status of the letter W “as a vowel”, we can no longer couch the discussion in imprecise, colloquial terms. Otherwise, the only answer we could give to your OP would be, “W is sometimes a vowel because the teacher said so.”
Bordelond Re-reading the thread, either I missed a few posts, or they weren’t there when I hit reply.
If I understand you correctly, the W in now represents an actual vocalized sound, and is arguably a vowel. The GH in night, while informing us that we’re dealing with a long I, is not voiced and is part of single vowel sound, and is not a vowel.
Bit Of A Hijack
Of the posters with knowledge of dipthongs and aspirants, how many of you are ventriloquists? It seems to me that with your knowledge of which sounds can be made without moving the lips, or visibly moving anything else, and your knowledge of what sounds can be substituted for these, ventriloquism would be a simple matter.
When I was an elementary kid (82-89) I (and most the people my age that I’ve asked) were taught that the vowels were A-E-I-O-U and Sometimes Y, no mention of W.
My younger sister had a teacher tell her that W was also sometimes a vowell.
I was SCANDALIZED. THE HELL YOU SAY! we all know the vowells, dammit, and there’s no room for W!
Well…I even went so far as confronting this teacher when I saw her several years later in a supermarket. I asked her, politely to explain it, and she explained it using the “interruption of air” method. I decided the poor woman was insane, and had no clue what she was talking about.
I grow up, do some reading on my own, and discover that yes, W sure CAN be a vowell. I remember the verbal beatdown I gave my sister when she repeated what her teacher taught her, and it’s one of those many reminders that know-it-alls, those who hold on to what they’ve been told without actually researching it, are usually wrong and make asses of themselves.
And so I now research stuff before I make an ass out of myself!
Of course, my sister went on to skip that grade half way through the year, Go to Havard, be elected student body president, and just this past year, made law review at Harvard Law. So, ya know, she got the last laugh as to who knows more. 
Steve
The simplest thing to say is that the sound that the letter W represents is sometimes a vowel, and sometimes a consonant. You know the expression “neither fish nor foul”? Well, W is both fish and fowl.
[QUOTE=DocCathode]
The GH in night, while informing us that we’re dealing with a long I, is not voiced and is part of single vowel sound, and is not a vowel.
[QUOTE]
I can’t follow you when you say that a sequence of written letters is “part of a … vowel sound”. My phonetic training gets in the way. IMO, the letter GH are there, but just as markers. No sound “belongs” to the sequence GH.
If I give an example from another language, it may help. In Portugese, the letter H can be a marker that either L or N are pronounced with a following “y glide” (cf. the difference between English canon and canyon, or Millen and million). But the H itself doesn’t “stand for” the “y glide”. Rather, the digraphs NH and LH, in Portugese are discrete, indivisible orthographic representations of [ny] and [ly] (which are considered single sounds in Portugese, not a sequence like [n]+[y]) – they can be pretty much treated as single letters, in fact.
Same with IGH in English. It serves as a discrete, indivisible orthographic representation of “long I” in English.
** fellow linguists: please forgive me for any bowdlerization above.*
We don’t count “borrowed” words, mostly. “Cwm” is a Welsh word, not an English one, although due to it’s popularity with Crossword puzzle writers, it is in the larger dictionaries. There are some foriegn words that don’t follow a Q with a U, but still in English, that’s a pretty solid rule. In Cow, How and others, W works as a vowel.
I’ll point out that Cecil has Spoken, and agrees with me- or perhaps rather I agree with him. 
As far as which letters are (OK, represent) vowels and which ones don’t, many of us were also taught that every syllable must have a vowel. But what about words like “rhythm” or “chasm”? If we insist that every syllable has a vowel, and that the only letters which represent vowels are A, E, I, O, and U (and sometimes Y, and maybe W), then we come to the absurd conclusion that “rhythm” and “chasm” are both one-syllable words. The much more elegant solution, I would argue, would be to admit that m can sometimes (as in those two words) represent a vowell. And once you’ve accepted that, it’s easy to accept that the sounds represented by F, H, L, N, R, S, V, and Z can also be vowels.
Or you could say that in “rhythm” and “chasm,” there is a second vowel, but it is not orthographically represented. It’s not so unusual. What about “Colm” in Irish?
The second vowel sound in “chasm” is unrepresented in the spelling. The [m] is the coda of the second syllable, not the peak.
That said, there are certainly occurances in human language when consonant sounds serve as syllabic peaks. In English, in a common American pronunciation the word “button”, the [n] is the syllabic peak (with a null coda). This can occcur because the tongue and lips do not have to change shape to pronounce the second syllable.
Link to a previous discussion about the nature of consonants, vowels, and everything in between.
Re: pronunciation of the Cantonese surname Ng (from the link above):
Ascenray has it down…except that
…I know that pure vowel, it’s prominently present here in New York City. (also in “Aww poor baby”, “lawyer”, “taught”, “bought”, etc.). But where I grew up in Georgia, those words are all pronounced with a diphthong and the lowercase C / open lowercase O sound you refer to is seldom voiced by itself down there. “Fought” would start off like “father” and then close down to the sound to which you refer.
You’re an IPA user, I can tell 
Grey areas abound, if for no other reason than our inability to enunciate certain sounds in certain sequences and make them sound different than (what we think of as) moderately different sounds within those sequences, even though in other sequences the distinction is more apparent.
There’s an Italian pizzaria-chain you’ll see in some northeastern public spaces: Sbarro’s. I challenge you to say it in a way that makes it plain that you are not saying “Sparro’s” instead. And yet we have no difficulty distinguishing between “Pete” and “beat”, “maple” and “Mabel”. Context counts for a lot.
IMHO, the IPA does a damn good job of trimming the whole works down to a manageable handful of symbols, seldom modified by diacriticals, each symbol having one and only one sound, each sound having one and only one symbol — all within the limits of context and our ability to distinguish sounds, especially those we aren’t attuned to, etc. I grew up with other phonetic systems, beginning with the classical American-dictionary version in which “long” vowels had lines above them, short vowels had curvy lines above them, and other diacriticals distinguished other vowel sounds (e.g., ä was used to represent the a sound in father and sometimes also the o sound in rot although sometimes the latter would be signified by ô).
IPA is clean and easy to use, at least for most non-EastAsian languages where pitch isn’t a factor.
I also recall as a young student in the early 1970s that my Phonics book had something on the inside cover saying the vowels were “a, e, i, o, u, and sometimes y and w.”
I also recall about ten years later, my sophomore English teacher told us that the only two English words that used w in a traditional vowel position were both Welsh derivatives: cwm and crwth, although I don’t remember what either of them means.
I can also never think of vowels without recalling a record I bought on the advice of the 1991 edition of the Rolling Stone Record Guide: “The Best of the Paragons”, an early Doo-Wop group.
It conains a song called “The Vows of Love”, which begins:
“A is for (something something),
E is for …”
It took me a second to realize this was an Ebonics play on words.
My understanding is that in Italian, “sb” is pronounced fully voiced, as [zb].
This is true for Italian, but does not affect the point AHunter is making about contextual phonetics in English. For the sake of an example, we can treat Sbarro’s as an English word.