Have you noticed that you’ve lost a good portion of your hard drive space ever sense you upgraded to OSX Lion? This may be due to a Time Machine feature that now does local backups when your Time Machine hard drive is not connected.
Why would Apple do this?
By creating local snapshots/bakups allows the user to still have the capability of going back in time to recover their files (all the benefits of recovering your files without the benefits of a hard drive crash). The average user that doesn’t utilize much hard drive space will benefit from this change, but users the use over half their hard drive space will suffer. In my humble opinion, Apple should have made this an option within the Time Machine settings.
Launch Terminal on your MAC: Applications > Utilities > Terminal
View the size of your local backup:
$ sudo du -h -d 0 /.MobileBackups/ 46G /.MobileBackups/
Disable/Enable local backups with tmutil.
$ sudo tmutil disablelocal
$ sudo tmutil enablelocal
You can also manually run a local backup:
$ sudo tmutil snapshot