every review i read the CF feature is just pretty much useless, its NOT worth the extra money, i mean the maximum % increase in performance is about 20%. which is pretty lame. here look at tomshardware vga charts and compare a single ati to crossfire ati cards.
EDIT: well i guess in games like oblivion the peroformance increase is way more than 20%, but you get the point, if you have enough money to consider Crossfire, DONT! get a 8800GTX.