I was also looking into the 3870...
Price wise... it seems worth it. You can look at it this way-
100 dollars more for an 8800gt... or... 100 dollars from from the 8800gt for another 3870.
I honestly think I may go ATI. The 9series is going to be $$$ when they first come out and I don't really want to wait too long for their price to come down although when they DO come out... maybe the 8800s will come down too?