I have my Mac's workspace down to a science-- everything is exactly where I want it and tuned just exactly how I think it should be. And so, even though it's a little silly, whenever a friend comes over and wants to use my computer, I always hesitate for just a second to let people invade my little workspace.
But now, those worries are over-- reader Michael C sent us a tutorial he wrote up for how to make the best use of Leopard's Guest account, and though he comes at it from a business' perspective, it seems like the perfect plan for letting my guests use my Mac without messing up my stuff. Basically, Michael walks you through how to log into the Guest account, and then how to save the settings you implement after customizing it (usually, they're wiped out on logoff, but his method has you backing up the defaults and putting your own in their place).
The only drawback is that any new accounts you create will use the same default settings at first, but I bet you could just load the backups and then create the new account and you wouldn't have any problems. And that's a very small price to pay to have a clean, configured guess account all ready to load up for anyone who happens to come over. Very nice!