I upgraded my 2G to the 3Gs. I'm very happy so far. The home button feels different, so that's a little weird.
But it really is faster. Even stupid things like the passcode screen are way faster.
3G downloading is nice as well. I like not having GSM noise near my speakers anymore too.
The new one still fits in my dock from my 40GB iPod from years ago so that's nice.
It will take getting used to not having the nice metal backing on it. However, I have yet to actually take a phone call on it.

Tomorrow I'll call my dad for Father's Day, so I'll get to test that part then.