If you find your Mac is running a bit more sluggish than usual, or a program you frequently use starts behaving oddly, you might need to repair your disk permissions.
To do this:
Open the Disk Utility by selecting Applications -> Utilities -> and then Disk Utility.
Select your primary hard drive (the one that you loaded OS X on) and then click the Verify Disk Permissions button.
Disk Utility will check your drive for any permission errors.
You may find a screen full of errors. If any errors do appear, click the Repair Disk Permissions button.