This is kind of a no-brainer hint, but I used Safari for a long time before figuring it out. If you want a psuedo button to clear all open tabs in Safari, create a folder in the Bookmarks bar and add a single Web site (like your preferred homepage), then select the Auto-Click box (in Bookmarks -> Show All Bookmarks), and name it something you like (I use "Clr"). Then you can click that bookmark in the Bookmarks Bar to clear all tabs and open the single designated page.
I find this especially useful with Taboo installed. Though I like Taboo's functionality -- I've accidentally closed windows with multiple tabs more than a few times in the past -- I don't necessarily like clicking through the dialogue box every time I intentionally want to close a window with multiple open tabs. Now I just hit my Clr bookmark before I close the window, or I use it just to clear all tabs and go back to my homepage.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050801231952743