I only tested in 2 games, Mass Effect 2, no drop on performance and it clearly "smoothed" some aliasing, although it also blurred a little bit the HUD and all the rest, but it was not to bad,
also on "Richard Burns Rally" (a 2004 DX8 game), it worked nicely to, made a big difference compared to no AA and I didn't notice anything wrong,

the VGA used was a HD5750 at default clocks.