Commercial exchange dwarf lady(East Gate): No matter how many times I try this quest, nothing happens when I reach the Moors(except maybe the 'encounter ended' combat log info). Equally as annoying is how she spams the "... they look stupid enough" dialogue every time you walk past her. No, dwarf lady, you're stupid, for spamming about a quest that doesn't work.
Whats-his-face that used to be called Noname(Farmlands) that gives the moms ring quest: Works fine, except that the weekly timer doesn't apply to it. I think you can do this quest every 24'ish hours. His dialogue spam also makes me want to murder him.
The guy inside the Merchant League(Docks): Pretty sure I haven't got that one to work a single time. Can't recall 100% if the 'encounter ended' thing showed, but I think so.
Dobran Stillface(Beregost): See above, regarding spam. I'd rather kill him than the badger, TBH. Of note - this quest will not work if you've finished the Radger the Badger quest recently... it took me a dozen tries to figure that out, and I laughed at the XP awarded for turning in the badger head.
Rescue someone from the Well(just north of the bridge to BG): Never works. It doesn't even say encounter ended. Unless I'm missing something... I've scoured down there and found nada zip zilch.
Various FAI interior quests: They work 80 - 90% of the time.
Various Candlekeep quests: Haven't managed to finish one yet, although I've only tried two or three times.
Refugee rescue(S. of Beregost): Works pretty much every time. Although, you better have an extra invisibility spell handy, and keep your companion quick commands hotbar'd if you don't want the guy you're supposed to rescue suffer from AI failz, and charge the xvarts like a dumbass.
I'll plonk around with the ones that keep borking.
PS. No, seriously, I hope the proximity dialogue for some of these NPC's gets axed. Turn their names yellow, or something
** Late edit - FYI, one way to stop the NPCs from yammering is to take their quests, and not try and complete them. This, however, prevents other characters from taking these quests.