This is from one of the previews....
Graphics look like they're still being optimized. The rig they set me up on was a powerhouse--a Dell 3.4GHz packed with an ATI X1900 512MB card. The video settings were set at a modest 1280x768 and anti-aliasing was turned off. There were some occasional stutters, and I could (albeit on rare occasions) see some stitching lines between textures. Performance seemed pretty similar for this machine as it was for the Xbox 360s running Oblivion on the other side of the room.
Glad I preordered the 360 version
impressive stuff for a console being compared to a X1900 system.