To make long story short, I restored my entire HD from Time Machine backups by selecting the HD in the Star War display and clicking Restore. After the restore process was done, the HD Used space doubled (according to command+I). It went from 100GB to 213GB. I was on the phone with Apple tech support for over 90 minutes. The case was escalated to the second level support but the problem remains unsolved. I will be calling the tech support back to continue where we left off. Meanwhile, any suggestion will be greatly appreciated. This is a 2011 MBP shipped with Lion.