In Drenchfort, there's a room with a giant statue in the middle and a place where you need to roll two balls into the holes on either side of the statue to progress. The ball on the right when you enter the room is on a ledge. I pushed the ball off the ledge and it got caught up in the terrain. No rolling, no shooting, no stabbing, nothing was getting this ball to move. Worse yet, the game autosaved when the ball fell, so when I re-loaded the game, the ball was still stuck.
The left side of the room has a stickybomb, but it's behind a gate. Well, long story short (too late!) I figured out how to dislodge the stuck ball and made a video in case it happens to anyone else: http://www.youtube.com/watch?v=4CEco7AjXfE (If this wouldn't have worked, I'd have to delete my save and start over) I've seen some other potential game-breaking glitches on youtube to avoid too.
If anyone runs into other problems, can you post it here? (I'm on PC, FWIW) Besides this potentially game-breaking bug, I'm having a lot of fun with the game. :D
tl;dr watch where you roll the ball off the ledge in Drenchfort.
edit: Just noticed a few other glitch threads, will check those out.