I “go with” whatever my natural inclination is. If in my idiolect a word is pronounced ‘correctly’, I keep pronouncing it that way. If I pronounce a word non-standardly, I stubbornly keep that as well. I’ll change my pronunciation of a word if it’s something I’d never really heard correctly before, but if it’s a word I grew up with and I know I ‘mispronounce’ it, don’t hold your breath.
The only word that I know the “preferred” pronunciation to, but say the more common one is “coitus.”
Seriously, it’s “supposed” to be pronounced “Ko-ee-tus”. Sounds ridiculous.
Regionalisms, I don’t count. Language is fluid, and words borrowed from other languages change pronunciation, and that’s fine with me. I know how to pronounce the name of the writer “Goethe”. That doesn’t change the fact that the name of the street in Chicago is pronounced “GO-thee”. Similarly, if I’m talking to a French person about things living in expanses of grass, I’ll say “des plaines.” If I’m talking about the suburb to my west, it’s “Dess Plainz”.
I run into a lot of mispronunciations of Wiccan and neopagan terms by newbies. I remember when I was new, and did the same thing and how embarrassed I was, so I do correct them, but only by the gentle “repition of the phrase with the proper pronounciation replaced” method. Like: “Hey! That was a great ritual, I’m so glad I charged my ‘a-thayme’ in time for ‘Sam-hayne’” “Yeah, that’s great. It’s a beautiful ‘athamay’ and I can’t wait to see you at ‘Sow-win’.” Only once have I experienced a girl too dense to get it, so I finally pulled her aside and gently told her it was “shee”, not “sid-hee”. It’s totally understandable, since most of us at least start our learning from books, but pronounciations of some of those words really are shibboleths that determine how seriously you’re taken by other practitioners.
I only “go with it” if -
(1) it’s a local place name
(2) it’s a family or personal name that they pronounce that way
(3) I have reason to think I won’t be understood otherwise.
I’ve got to agree with Lama Pacos. ‘Lie-bree’ is how I say it (and it rhymes with ‘cutlery’ 
). That’s how everyone with my accent says it. And it’s listed in the Cambridge dictionary as a valid pronunciation.
Should I tell my pupils that the way they pronounce such words is ‘wrong’, even though I say them the same way, just because it’s not how everyone in the English-speaking world pronounces them?
Ever been to Loughborough? 
It’s acceptable to pronounce comfortable with three syllables, and with the “r” after the first “t.” And how the heck does anyone find 3 syllables in Wednesday?
Acceptable doesn’t make it right 
I patently refuse to pronounce Wednesday as “Wenz-day”.
I’m all for the natural growth and mutation of a language through common usage, but I consciously avoid participating in the “lazification” of English.
What she said.
I will, however, correct people who mispronounce something in the course of trying to sound more educated than they are – especially if they’re trying to use a foreign word/term (assuming, of course, that I’m sure of the correct pronunciation myself). In such cases, I find that they often don’t know the word’s definition, either. I’m just too pedantic to let that kind of thing go.
I was always taught that words (including place names) in radio copy should be spelled phonetically in the first place – or at least spelled the way they’re pronounced!
I can’t stand what I think- at least in my part of town- improper grammer of “gone missing”, or “went missing” especially since tv’s *Without A Trace * everyone and the newspaper ect use it!! It is just IS missing, **HAS BEEN ** missing since… If someone is gone, they are gone,or they are missing, are they both at the same time?? And went missing??? My third grade english teacher Mrs. Robinson (really her name) would have puckered up if she had heard any of us say that? Horrors! I cringe every time I hear those two phrases spoken!!!
Just out of curiosity, how do you distinguish between laziness and efficiency? If one can convey the exact same information with less articulatory effort and without raising (most people’s) eyebrows, how is that lazy rather than efficient?
So what does make it ‘right’?
How about ‘wens-dee’? 
This was in the day when the boss was right and you were wrong. Period.
An interesting question, and one difficult to quantify.
At best, I can give an example: this very message board’s proclivity to thrash anyone who doesn’t use/overuses their shift key and/or abbreviates unnecessarily (you = u, etc.).
Both usages are technically more efficient, because they require less keystrokes, and convey the same message, yet they are both universally derided. It isn’t because everyone is against efficiency, but rather the obvious lack of effort or (dare I say?) pride.
So, while I’m not necessarily opposed to the growing acceptance of the dropping of the G sound from words ending in -ing (for example), I am opposed to dropping entire syllables to accomodate “mush mouth” pronunciations.
To each their own I suppose. My vocabularistic instincts guide me (and allow me to make up new words with reckless abandon).
Apparently we Brits can get away with more 
… http://dictionary.cambridge.org/define.asp?key=51102&dict=CALD
Who said they’re being ‘dropped’? What if it’s an alternative pronuncation, which you are unaware of, but which has nonetheless existed alongside your familiar one?
I have a friend named “Jim in nez”: Jimenez and another named “Morris”: Maurice. 
I’ve got a fairly unusual spelling of a fairly common name. I don’t bother with the ‘authentic’ Welsh pronunciation, because it only works with a Welsh accent, which means that even I can’t get it right. On the other hand, Welsh people can and do pronounce it that way, and when my Irish relatives pronounce (or spell) it their own way, I don’t have a problem.
It’s a fair assumption that the longer pronunciation would be the original and correct pronunciation, and that the alternative version is a later invention, as I don’t imagine there is much precedent of words evolving to become longer through common usage.
But that’s not how he pronounces it. For him, it’s “lie-berry”; you know, strawberry, blueberry, lieberry. He’s an educated guy. He should have stopped saying that in third grade, the same time he stopped saying “pisghetti”.
I have an uncle “Morse” spelled “Maurice.”
While there’s linguists on the board who may offer more informed opinions, I don’t see why this is a fair assumption - because it relies on the inital premise that there is a single root pronunciation from which all present ones are derived.