I'm using Windows 7 just like you all. Ultimate edition, 64-bit. The system is running perfectly without any problems, but I got one issue after two weeks of using Windows 7.
The problem is that video preview thumbnails are not showing up. "Show thumbnails instead of icons" in view options is checked.
Take a look. On the left side is my HDV camcoder captured files, .mt2 format. But on the right side is my video folder, contains .mp4 and .wmv formats. As you can see .mp4 .wmv thumbnails are missing.
Maybe this is the place where I finally will got the solution.