I'm eligible for an upgrade, and I've wanted an iPhone for 4 years. This is the first time I could get one on Sprint, so there was no reason NOT to get the 4S.
Because I currently own a Droid 1 from Motorola... need I have any more reason than that? hahaha... it's such a POS, I can't wait to be rid of the thing!
Mine would be:
1) my 3g is at end-of-life (and my patience)
4) my 3g is making me violent
7) my 3g needs to die peacefully