G-dropping

I read somewhere that G-dropping in, say,

they've been buildin' it for ages - sounds okay
but - they walked into the buildin' - is wrong

Is it true?

Are pronunciations like mornin' and weddin' completely substandard?

mornin' is standard, weddin' I probably wouldn't even understand. It seems to depend on the word itself.

Why would you drop Gs in the first place?

I have no problem saying "getting" instead of "gettin".
It's just that the latter is kind of, well, more natural for me.
I'm just used to it.
I don't say "rin" for "ring" or weddin' for that matter
(i was just curious cause I heard weddin' in a song once)
I know some people have a problem with G-dropping,
they think it's vulgar and stuff, I don't though.
That's why I say things like "durin' the party" and "it's gettin' late".

<<but - they walked into the buildin' - is wrong>>

It's not a "building", but a "built" unless it's still being built.

So Bob, you confirmed my suspicions about weddin'.
But what about words like feelings (n), meeting (n), during?
or collocations like "training day" or "I don't feel like studying"?

I wouldn't drop any Gs of nouns.

If I am speaking very informally I drop nearly all the g's, but if I am speaking very formally I don't drop any. In situations in-between, such as interactions with co-workers and retail personnel, I am less likely to drop g's in words used as nouns, in less common words, and in instances when dropping the g would result in a syllabic n.

I only rarely notice when somebody drops or retains a g in a situation when I would do the opposite. That makes me think that either I'm typical or that usage varies so widely that I just don't notice. Of course it could just be that I'm oblivious and everybody snickers behind my back whenever I drop a g.

Occasionally I meet somebody who uses a very odd-sounding hybrid of dropped and undropped g's, so that going sounds like goeen.

Obama is a situational 'g' dropper (along with all the other things he has dropped).

Thanks, Jeff