I usually play on Ultra quality, 1024x768, 2x AA, Vertical Sync ON. I get around 37fps in the timedemo, if I turn the VS off I get around 45fps.
Generally though the in-game framerate is pretty steady throughout; 55-60fps. Drops in certain areas, but still very playable.
AMD X2 4400+ Toledo 1MB/Asus A8N-SLI Deluxe/2GB Kingston HyperX/SLI Gigabyte 7800 GTX 256MB/Creative SB Audigy 2 ZS Plat w/ Creative Inspire 6.1 speakers /180GB Hitachi PATA/19\" AG Neovo F-419 LCD/OCZ PowerStream 600W PSU/WinXP Home SP2