|Superfetch/Readyboost||Readyboost device inserted, first run, when Vista analyses that you use particular programs/data regularly.|
|Indexing service/Windows Search|
Assumed after every new file write/delete - reindexing for greater index performance occurs randomly (well, when the index needs cleaning up).
|Windows Defender||Periodically in the background, automated scheduled scans.|
|System Restore||When a new driver or piece of software is installed.|
If you have Vista on a laptop and use Readyboost (via built in card reader or similar which I do), I'd recommend leaving Superfetch/Readyboost enabled, and System Restore for obvious reasons. I've disabled Windows Search via the services (because of heavy disk/battery usage) and Windows Defender as I'll enable and use this manually when I need it (I don't need it bugging me every 3 days/running whilst I work).