Many people have asked about creating bootable backup of OS X. Over in the MacFixIt forums, there was an interesting conversation about this a while ago. In this thread, "Sparky the Wonderpig" gave a fairly simple solution to the problem ... more interesting are comments from other posters concerning how it may be addressed by a future update from Apple.
If you're interested in backing up your OS X volume now, check out Sparky's method ... and let's hope we see an official tool from Apple soon!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010827220623519