A great tip from my friend Liam Colvin:
I don’t know if you’re like me but I was experiencing slowness (like a 20-30 second delay) when opening an Explorer window to view files. You might have found this before me, but it took me some time fiddling with settings to figure it out.
I was trying all the usual ways to determine what was causing the delay in opening the explorer window: anti-virus, explorer extensions, etc – and nothing worked, very frustrating.
I looked extensively internally and searched the Internet, and the best I could find were issues with copying files down from servers causing delays due to SMB issues (there is a hotfix out there for that, by the way – http://support.microsoft.com/kb/931770/en-us).
I finally found it after carefully reviewing the behavior of Explorer when it opened by monitoring the Explorer process with Filemon. I noticed that when Explorer went to open a folder (from a shortcut, for example), it parsed all the files in the root of the directory. Urk! This clearly took a long time.
I looked at the Folder Options under Control Panel and noticed the very first setting under the View tab: Always show Icons, never Thumbnails. It was not checked. I realized that Vista must read each file when opening the folder for a thumbnail and/or creates one. When I checked the Always show Icons, never Thumbnails, it reduced the time required to open each folder to 3 or 4 seconds.