When I got back in, first thing I noticed was it put me back at the entrance to the area I was in...field of something...? Can't remember offhand what the area was called, but it was the first overworld section following the defeat of the Skeleton King. Then I looked at my map, and it was completely empty, except for the part I was standing in, and just a small part of the town. The teleporter locations were visible, but nothing else was. Everything else had also reset. Monsters were all there, everything I'd broken (tombstones) was restored, even the small dungeons were reset. Only things that didn't reset were my progress through the act and the achievements I'd gained to that point.
Something tells me that massive reset of the area was NOT supposed to happen, but I'd like to hear from somebody, preferably from Blizzard, on whether this is supposed to happen or not after the game locks up to where you have to force it to close in order to continue playing.