Having spent the weekend playing all of my games with one card, then two cards I would say it's worth it.
I upgraded my core system so I think that really helps, the new SB setup is much faster than the old dual core.
I just finished playing Crysis at 1920 x 1200, very high settings and it was very fluid and nice. I would say that if you love to crank your games with everything maxed, it's a fairly cheap way to go. I didn't see any microstuttering at all, that was with some games vsync enabled, some not.
Btw I played Crysis, Borderlands, CoD-BO, CoD4, LFD 1 and 2, Just Cause 2, Fear 2, and some Bioshock.