Every time I look at the used and unused space on my HD, the used amount is growing. I shut down last night with 74.5 gigs used, and woke up to 80.2 used.
This has been going on for a week since I installed Vista and W7.
Did the virus checks and the rest; Chkdsk/f  etc.
Finally I did some googling and found what appeared to be the answer. (AND IT WAS)
The automatic restore points were being saved on every move made; boot up, shut down, add a driver, change a driver, add an app, update a program.... and saved with files, your files.
I only have Vista running for 9 days and it grew 20 gigabytes. I know, because I did the shut it off fix, and retrieved 20 gigs of hard drive space.
I shut off the auto restore point maker, but there is an alternate method where you can allocate small amounts of space instead of 15% of your hard drive which is default.
Alt Method...http://www.downloadsquad.com/2007/04/20/hot-to-reduce-disk-space-used-by-windows-vista-system-restore/

All I did in the meantime, is to right click on MY COMPUTER, then Properties, then in the left panel, System Protection. Unclick the check in the drive letter, and then click APPLY... might be an additional button to click on some versions that says, removing stored restore points.
Poof! I got back 20 gigs that was purloined in just 9 days.

I will check my W7, but it is likely similar.
PS I can make initiate manual restore points any time I am installing a new video driver, or some software update that is suspect... etc.

Fred

Terry,
Did you click the link in my post?
That fellow seems to have included the answer in his article.
XP never saved files, just restore points, so space was not an issue.
In Vista, it is an Issue.

It isn't the restore points that bother me, it's the files that Vista saves with the resore points that build the used hard drive space.
I can make restore points manually when needed, or, since it's so easy to turn the auto restore on and off, I can do that, or I can set the space at 2 gigs for the restore space.
In a sense that would prevent the drive from being overrun, but I'll bet that 2 gigs of space is too small.
I know one person I spoke to today who recovered 103 gigs when he killed that auto restore in his Vista.
I do Acronis complete hard drive image backups almost every night. I can always rely on that method if need be. Restore my computer to last night!
To each his own...
Fred

Terry, et al
I did a little poking around in W7 last night... Mind you, all above is related to Vista.

The interesting part is that they have sort of corrected the situation in W7
by making an obvious slider where you select the HD space for Restore
Points.
It tells you right in the open when the size limit is reached, the oldest
restore points are deleted.
That, we all can live with.

Fred