When you move your mouse over a taskbar application in Windows 7 or over the outline button in the lower-right corner, previews show up in about half a second. Customise that wait time with a quick registry hack.
At his home away from Lifehacker, the How-To Geek details the registry value that sets the millisecond wait time on Aero Peek previews — the kind that show application window previews and window outlines. Its default is 500, but those with snappy systems can go all the way to "0" for instant graphical effects, or those who dislike the drag on their graphics card can pull it up higher.
The value, for adventurous, impatient registry hackers is DesktopLivePreviewHoverTime; for a much more detailed walkthrough, hit the link.