Re:easy. (Score 1)

create a guest account.

I agree. Note that if you're running a recent version of Fedora, there's a built-in 'xguest' SELinux profile which is completely locked down -- that might interest you, along with the fast user switching.

Yep, and OS X 10.5 has a similar Guest account... you turn it on through the Accounts panel. Once enabled, it adds a 'Guest' link to the login page - clicking that creates a temporary user profile (totally restricted of course) which is completely deleted when the Guest logs off or the machine is shut down. Only downside is that it's quite easy to click by accident when trying to log in with your own account - and because it doesn't require a password, starts the login process immediately!