I've tried Skyrim on GTX295 and on two 560 Ti in SLi. Installed to an SSD drive, 8GB RAM, Windows 7 64-bit, and an i7 2600k. Everything running at stock speeds in 2560x1600 resolution.

With all settings on Ultra with the exception of Shadows, which are set to high, you can expect to get a minimum of 45-60 fps only capped by the vertical sync. Runs as smooth as butter. On that note GTX 480/570/580 will likely be able to run this quite well in any lower resolutions with lesser hardware.

Hope this helps those looking for some idea of performance and wondering if they need to upgrade hardware, as I was contemplating yesterday.

Enjoy the game!