Disk clean up is different for every computer so no one size fits all really. What is usually safe to delete are things like Temporary Internet Files, Recycle bin files and Temporary Files beyond that it depends on what is on the computer and what you really would rather keep, so things like if you have the option for Thumbnails to delete it will recreate these the next time you use this feature. On the More Options tab it brings up Add/Remove Programs and the option to delete all but the most recent restore points, if you have been ok and find you wouldn't need to go back to much more then a few weeks ago it should be safe to delete older restore points.
To check and see if you do have hibernation enabled click on the Start button then Control Panel and then Power Options, Change Power Settings for the Power scheme you are using then Change Advanced Power Settings, you can see if there is any reference to hibernation in those settings.
Hope this helps,
Northlite
I am trying to figure out what are the standard or best deletions to check off under disk clean up. I
hesitant am to check off ones that I might regret. Is anyone confused about hibernation? I noticed that when I tried to delete that in disk cleanup it would not clear.
I do not believe my system is set up for hibernation, but I am new to vista and this feature. I would appreciate any feedback,
Thanks, Marc.

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