I have one; it's great. It's not a shit ton faster than my old 9600GT, but it was worth the money based on speed alone. That's the thing, it was like $140 or something after rebate (scam). Sold the 9600GT for $65 I believe (thank you SLI for creating a market for used video cards). Hell, I did the same thing when I bought the 9600gt; got it for just over a hundred and sold the 7950 or whatever I had before that for about $60. Oh, and the 5770 came with Dirt 2...which is awesome.
But yeah, I like the card a lot (even though ATI still doesn't compete with Nvidia with their driver support). Runs fast, quiet, and I didn't have to get a new PSU. Bad Company 2 and Dirt 2 both utilize DX11, which actually seems pretty sweet. BC2 only uses it for soft shadows aparently, but they look great and don't really have a performance hit...enabling me to turn off AA at 1680x1050 (or I could leave it on because the game seems to use the CPU waaaay too much and that's what's limiting my frames anyways).
Dirt 2 uses it as well and runs great. It takes advantage of more of the DX11 features, like something to do with better shader programming or something (in over my head here, but the night courses in Dirt 2 look quite a bit better in DX 11 because of how it handles the interaction between the sand and all the lights). The main thing, however, is we finally have official DX tessellation support...which I imagine will be used quite a bit.