See article here:
http://news.cnet.com/8301-13880_3-9862223-68.html

If you have "Show Hidden Files and Folders" turned on (see Tools>Folder Options>View tab...), you'll see a bunch of Uninstall folders (in blue text, with $ signs) in the root of your C:. You can delete these files. These are the uninstall files for Windows Update, that allow you to roll-back your system if an update doesn't compute with your system. I decided to remove mine since my computer is fairly new and I don't see a risk of not being able to uninstall an update I've done through Windows Update.

Anyhow, I deleted my folders, totaling approximately 2GB.

The article above does not state this, but I found this via some research. I left two folders, one being "$hf_mig$", and the folder "ie7" (which is in blue, yet doesn't have a $ sign or "Uninstall" in the folder name). I was told the following folders/files will be needed in future updates. I kept those two folders.

Thought this tactic was interesting, especially since I help maintain a netbook that has an incredibly paltry hard drive, and this really helped free up some space.