Everyone agrees, that Time Machine makes your life a lot easier. Did you know about the fact, that programmers are able to integrate it into their applications?
For example, open iCal and click on Time Machine in the Dock. Now you are able to move back in time and restore deleted or changed entries. Sneaky. 
But the fun does not stop here, you are able to restore mailboxes as well. The mechanism does not work with RSS-Feeds in Mail, though.