So the conclusions I'm drawing from this are:
there are some scenes, where a slip or dropped weapon can add tension
these scenes can add comic relief (not all combats are dead serious, many Jackie Chan fights are funny)
fumbles that have deadly effects should probably be avoided (particularly self inflicted decapitations)
The mechanic and tables used can impact the value of a fumble system
critical fumbles on attack rolls may be an imperfect mechanic (high level PCs are exposed to them too frequently)
Some of the 3e rules and combat actions may replace some of the fumble-effects. Disarming, tripping, sundering for instance are actions the enemy can take against you already, whereas in the old rules, they weren't.
A couple of thoughts considering the rules (not specific rules, just concepts):
basing critical fumbles on attacks alone has the following faults:
you can only fumble if you make an attack roll
if you have multiple attack rolls, you have more chances to fumble
The "Critical Events" table from the 2e Combat and Tactics (the 2.5 precursor to Skills and Powers) had an interesting take on things. It generated events each round, independently of what the characters were doing. Assuming the table made sense, this seems more "realistic"
A random action list for NPC opponents might be interesting. Given the choice of cool actions, and NPC can take, how often does a DM just slug it out with the PCs. Why not mix it up a bit (and a table might help get the DM out of the rut). For instance (this is just a made up table):
1. Fight Defensively
2. Sunder the enemy's weapon
3. Try to trip the enemy
4. try to disarm the enemy
5. back off to a new position
6. flee
7. Full attack, with 5' step
8. Full Attack, hold ground
Maybe some more entries for Full Attack, so much of the fight consists of attacking, but with chances for the enemy to try some other tactic.
I think part of the goal of fumbles, is to inject events into the game that the PCs must deal with, making it more than just trading blows with the enemy. In which case, there are numerous methods to do this, not just for rolling a 1 on an attack roll.
Good discussion folks. I like how many of you found examples where fumbles occur, and weren't just for comedy.
Janx