The exploding termsheets
http://ycombinator.com/exploding.html
have started to arrive. I just talked to a group who got one, and they hadn't realized we were willing to interview groups early when this happened.
So I should be more explicit: If you get an exploding offer, send us an email, and if we were going to interview you, we'll do it early.
I recommend you consider that signing a term sheet is like entering into a relationship. Do you want a relationship with someone that's behaving badly beforehand? They're already on their best behavior.