I just recently upgraded from an iPaq 3835 to the Dell Axim X3i. I really like it.
I agree with Hantra - the WiFi setup was extremely painless for me as well. I previously had an expansion pack and a CF card for my iPaq. That required some minimal setup to get connected. The built-in wireless on the X3i connected almost immediately upon activation of the wifi - no setup required!
Battery life is strong. The screen is bright. I don't know if I'm sold on the cheesy stylus Dell gives you - that's cheap and easy to fix though.
After about a three weeks I can't find anything wrong with it. All in all, a great PDA.