Tab saver, too

Tabbed browsing—which lets you open multiple Web sites in a single browser window—is a handy feature. It’s been available in some Web browsers as far back as the mid-1990s; Safari finally added it in 2003 (in Safari 2.0). However, tabbed browsing introduces a potential issue not found in one-page-per-window browsers: the risk of accidentally closing a window with multiple tabs when you really just wanted to close a particular tab—or accidentally quitting the browser when you meant to simply close a tab or window. If you’ve got ten Web sites open in a single window, and you accidentally click on the window’s red “close” button, or press Command+Q instead of Command+W, you’ll lose all those tabs, with no way—short of racking your brain or weeding through your browser's history—of getting them back.
http://www.macworld.com/weblogs/macgems/2006/08/forgetmenot/index.php