There are very few things that annoy me about Windows 7, but one thing that consistently does is the Alt-Tab behaviour wherein it will, after a delay of one or two seconds, start showing previews of the windows represented by the icons in the Alt-Tab list of running programs.
The main reason it's annoying is that it seems to start doing the preview just as I am scanning the list to look for the program I want. I don't need to identify it by previewing the window; I just need time to find the icon in the list so that I can hit Alt-Tab enough times to get there. The preview begins in the middle of this effort and distracts me from what I was searching for.
I didn't think there was a way to turn it off without disabling the Aero Peek feature altogether (which would also disable the useful feature of seeing through open windows to the desktop without having to minimize everything).
But, there is a way!
Using the Registry Edit, you have to create this key:
Inside that key, you add a DWORD value named:
...and you set its value to 0.
When you restart Windows Explorer, it should take effect. You can either log off and log back on to kill Explorer, or open Task Manager, end the EXPLORER.EXE process, and then use Task Manager's File -> Run to run EXPLORER.EXE.