I've kept my 2G because it is usable in both the US and Canada (via, um, magic fairies).
It runs everything I want it to run, works great in both countries (I tend to travel only to sizable cities), and I'm in a wifi environment 90% of the time so the lack of 3G has never been a big issue.
Sure, I thought the compass and GPS and all that were nice on the later models, but it wasn't compelling enough to make me switch, especially considering that having finished my initial contract with AT&T I'm on PAYGO in both countries which is very inexpensive ($19/month in Canada, $25/quarterly for US).
The iPhone 4 is more than compelling enough to make me upgrade, but then I have to get a contract, which now REQUIRES a dataplan, for three years (Canada). That plus a planned iPad and a new laptop later this year ... that's a LOT of money. So I'm still weighing my options. In the meantime, the 2G continues to do everything I *need* it to do (and to my great surprise, most apps run on it just fine).