I just got the w810i today, and i'm loving it.
A really good review here:
http://www.mobileburn.com/review.jsp?Id=2310
Main differences from w800 (off the top of my head)
- Quad band
- edge support
- it's black
- no joystick
- w810 has less internal memory, but of course with memory sticks, doesn't matter too much.