Fumbles are an optional or house rule, most often used I'd assume by 1st edition players who remember the old critical hit and fumble tables. The most common rule I've seen is that if you roll a 1, you must roll a DEX check vs. DC 10 modified by the sort of things that effect balance. If you fail, something bad happens - you fall down, you drop your weapon, your bowstring breaks, you make an attack on someone other than your target, you make an attack on yourself, you become flatfooted etc. I find the 'something bad' to be a little vague, and would probably devise a table if I were using this rule.
I've never seen Croatian's fumble and critical fumble tables, but I'd assume that would be the sort of thing you'd be looking for.
Waking up requires a listen check, but you may only take 0. This means that essentially, anything better than your listen skill bonus beats your listen check. That is rather rude, since sleeping characters are helpless and your average 1st level rouge (or bugbear) would beat most sleepers AND at the least could certainly get within 30' of most any sleeper for a ranged sneak attack (provided he could see in the dark), but it's not far from reasonable. A less cruel DM might give you a -10 penalty on the listen check, so there was at least some chance of waking up vs. an averagely sneaky creature. Also, many DM's rule that you may only take a partial action on the round you wake up, even if you do wake up.
I've seen a really nifty Feat roaming about the net called 'Light Sleeper' that let you make a listen check even when asleep, and let you take full actions even on the round you wake up. It might be in the Net Book of Feats.
Gromm, I'm pretty sure that the difficulty for hearing combat is a good bit less than 0, something like -15 or lower, so that the average person could always hear the din of battle a good 100' yards away or more, or in a room on the other side of a stone wall, and so forth.