I've notice the same problem with my tv turner program (TotalMedia) when install on windows 7 from vista x64. At default vista looks real smooth quailty wise but on windows 7 it started to look like it all pixelated or something. I think it's more on the incompatibilties with certain software players and windows 7.
Here's how I fixed my problem:I right click on properties for that particular program and choose the compatibility tab. Under setting, select "disable desktop composition".
Just click ok to exit.
After selecting that for me the video quailty came out nice and smooth just like it was on Vista. Again I'm not sure if this will fix any of you guys problem but figure it wouldn't hurt to just try it. Thought I'd share this since it hasn't been brought out yet. Good luck and hope this can help solve some issues about Windows 7.
Edit: Earlier I mention to select "disable visual theme", I'm sorry I actually mean to select the one below it which is "disable desktop composition"