Have you ever opened up a folder full of tabs in Safari accidentally (ie by Command-clicking on a bookmark folder), which then overwrites any tabs already carefully opened in the current window? Don't sweat about re-loading all the links you were looking at previously.
Simply hit the Back button, and Safari will immediately close any erroneously opened tabs and revert back to the set of tabs you had opened before.
Simple, yes, but has saved me a couple of times!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030504065720641