With my 7600gt I was getting a constant 60fps but now I'm averaging ~30fps with the 8800gt. Any ideas as to why this could be and how to fix what's wrong?

Tell us your system specs.

I've recently picked up two 8800 GTS 512's coming from SLI'd 7900GTX's and have found that when setting the Antialiasing setting to "enhance the application setting" or "overide any application setting" instead of leaving it at application controlled - my framerate in certain applications suffers. As soon as I drop AA back to either 4x or Application Controlled - in certain applications (COD 4, Oblivion, Crysis especially!) my gameplay is fluid, fast and back to normal. I believe it has to do with what's called CSAA (Coverage Sampled Anti-aliasing). CSAA is supposed to give you the quality of either 8x or 16x AA, but at the performance impact of 4x AA. If my understanding is correct, if a game doesn't have an AA profile programmed for CSAA, the Nvidia driver is supposed to default back to 4x AA. At any rate, its caused really choppy framerate for me. So if you have your WOW profile in the Nvidia control panel set to enhance instead of app controlled, try switching it to application controlled and see if that helps.

I actually had it set to 16x and I got a flat 60fps but everything looked jaggier (can't understand why setting higher AA would do that) it's when I turned that off that I started getting the bad framerate.