A message kept popping up my system telling me my C: drive was low on space.
After ignoring it for a while, as I am prone to do, I finally decided to do something to stop it, lest my right eye end up with a permanent twitch.
Easy enough, I figured I'd just use the Windows Vista utility Disk Cleanup.
Once it came up, I was presented with the selection box of the files that I could delete to get disk space back. I decided to be very aggressive with my choices on which files to delete and checked nearly everything, including the checkbox on Hibernation File Cleaner, not fully understanding what cleaning the hibernation file would do. (The screen shot is an example, mine actually showed nearly 20GB of recoverable disk space)
All went well, I recovered GB's of space and I felt better with myself. Later that morning when I decided to hibernate my laptop, I clicked on the Start button to hibernate my system only to find I had no Hibernate option. That can't be right. Poked around..sure enough... no longer an option.
Hmm, checking around I found the Hibernate File Cleaner actually removes the hibernate file, and when that happens the Hibernate Option gets disabled. Doh!
To get Hibernation back I simply had to re-enable it by bringing up an elevated command prompt entering:
powercfg -h ON