Does Time Machine check that old backed up files are present and not corrupted? My only copy of my (large) iTunes library (and all my personal files) is on my MacBook, and I was thinking about using Time Machine to back it all up to an external hard drive (a Western Digital MyBook plugged into the USB port on my Airport Extreme).

My question is, when Time Machine makes a copy of a file (say, a song) to the hard drive, since that file never changes I'm guessing it will never get updated by Time Machine.  But will Time Machine regularly review the file to make sure it had not become somehow corrupted?

I've had trouble with hard drives going bad in the past, and I would hate to be trusting Time Machine for a months and months only to find out that some hard drive partition got corrupted and the file was actually gone long ago.

Any thoughts?
If you hold the "Option" key while clicking the Time Machine icon in the menu bar, there is an option "Verify Backups".

If the Time Machine icon is not in your Menu Bar, go to System Preferences, Time Machine, and tick the "Show Time Machine in Menu Bar".

I can't see any other way to get to the "Verify Backups" other than through the item in the menu bar.