Location: Farmer's Cellar in Act 1 - Fields of Misery
Character: lvl 11 Demon Hunter + templar

Event: Entered the cellar, spoke with the farmer and his skeleton wife, and gathered loot. Then the game seemed to lose synch like in D2 when your character got stuck on an object but the client didn't realize it until you backtracked and figured out where you were stuck (which didn't work in this case). Couldn't loot, interact, leave area, town portal, or even leave the game from the menu. Minimized and verified connectivity. Eventually had to exit the game (which also took a significant amount of time, but did end up completing by the client) and relaunch, which deleted progress back to the last quest completion.
Edited by Draijor#1309 on 5/15/2012 7:42 AM PDT