Well not sure about the demo but I have been playing the full version and it looks awesome, plus it plays pretty good as well.
Very similar in graphics to Dirt, so close that it is hard to say one is better than the other, but if I had to give a winner Grid would be it. I really like the Le Mans race that takes the 24 hours and turns it into 24 minutes. You start in the day and race into dusk, night, dawn and back to daytime. It just looks so good as it is getting dark and as the sun begins to rise in the dawn.
I currently run it at the highest ingame settings @1680x1050 and have no issue with frame rates. Not sure what they are as I haven't run fraps or anything while playing it but it is good enough not to hamper game play. Oh and that is only using one of my 8800 GTs as I don't have the SLI set up in Vista currently.
All in all, a really nice racing game. Now I just need someone to make a really good combat flight sim for the PC.
Edit: After playing around with the settings a bit I have found what is pretty much the limit with just my one card in Vista. Everything is maxed @1680x1050 and the multisampling is set to 16XCSAA, at those settings I get an average of 52fps with a min of 40 and max of 63. Now if I move the multisampling to the highest option of 16XQCSAA it brings it to a crawl, average of 6.1fps with a min of 4 and a max of 17. And that is running the exact same race with the same cars. I have yet to see how well it scales with SLI but I just might have to give it a try.