Meh... Noisy, bad driver support (worse than ATi itself... WOW) and about equal performance to the gtx280. Not to mention the fact that 2 cores on one card are harder to custom cool with air.
I was once hoping to go 4850x2, but now the only option I would remotely consider is another 4850 or a gtx260 216.
EDIT: good review though ^^