Great ideas everyone. Chainsaw - yeah, I can totally see that. Like I said, I've done the mega-dungeon thing, so, I can see it being a blast. I certainly had fun with it.
I'll give you an example of play grinding to a halt and see what you guys would have done.
In a recent campaign, I was playing a rogue (4e). The party was dungeon crawling and found a room where there was a trap - a pair of brazier's on tracks that would advance slowly down the room, shooting jets of flame between them at intervals.
Now, during the fight in the room, this trap was a factor and very interesting. But, after the fight was done, we wanted to disarm the trap so that if we had to run away, we had a clear line of escape. So, being the rogue, I proceed to disarm the trap.
I roll high and look expectantly at the GM. He looks back and says, "Well, what else are you doing?"
"Um, what?" I reply.
"Well, the trap isn't disarmed yet."
"Um, what? Err, did I fail my roll?" I'm confused.
"No, you succeeded, but the trap is still active."
Now, this proceeds a few minutes of fumbling around, with me totally confused. I detailed that we jammed swords into the tracks to block the braziers and... ummm... tried to break the mechanism... uhh ... uhhhh...
What had happened was that the GM had decided to turn disarming this trap into a Skill Challenge but hadn't actually informed us of this fact. So, the group (everyone else was just as confused as me) was playing one game and the GM was playing another.
We wound up spending about an hour fumbling around until we finally managed to disarm the trap. A trap, I might add, we didn't really have to disarm in the first place, but, we had disarmed it as a precaution. We could have just as easily left it.
Afterward, I questioned the GM about this, wondering what was going on. I was rather frustrated by this point and perhaps less polite than I might have been, but, I'd just blown about an hour on something utterly pointless, so, I wasn't really all that cheerful.
He replied that he wanted the skill challenge to seem natural. To announce it as a skill challenge would have broken immersion in his opinion.
And, really, I can see his point. It probably would have.
But, at this point, IMO, pacing is more important. Wasting an hour on something totally trivial is not worth preserving five minutes of immersion.
What is more important to you?