My notebook was down to the last 800MB of disk space. Amazingly I just claimed back 17GB through Windows Vista Disk Cleanup!
The big wins were:
- It turned off Hibernate functionality for me - which I never used (3.4GB)
- It got rid of a bunch of dmp files from when I had some driver issues causing stability problems a few months back (1GB ish)
- Temporary files (2GB ish)
- Shadow files and restore points - a huge 8GB!!!!!!!!!
Very sweet (although I wish Vista had advised me to do this a while back).