Speed up Windows 7 Aero Peek Thumbnail preview display

The default for the Tasbar Preview Hover Delay is 400 milliseconds. To set it follow these steps:

Here are the steps:
1. Click on the Start Button and type in Regedit and hit Enter.
2. Navigate through HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced.
3. Right click on Advanced and select New DWORD and name the new value "ExtendedUIHoverTime".
4. Right click on ExtendedUIHoverTime and select Modify.
5. Switch to Decimal base and enter in your new number. The default is 400 milliseconds however I recommend 200 or 100.
6. Once changed click OK and restart the explorer process or restart your computer.

Additionally.... 

I found another site also that let's you set this globally for all hover system times (Tasbar Icons, start menu, shortcuts etc....

1. Click on the Start Button and type in regedit and hit Enter.
2. Navigate through HKEY_CURRENT_USER\Control Panel\Mouse.
3. Right click on MouseHoverTime and select Modify.
4. Set the new value. The default value is 400 milliseconds.
5. Once changed, click OK and restart your computer.

Have Fun!

Sources: http://forum.groovypost.com/windows7/speed-up-windows-7-aero-peek-thumbnail-preview-display-t95662.html