Gmail user Kevin Gunn creates web site specific addresses and sets up filters for them to catch companies who spam or sell email addresses of its customers:
Let's say you need to sign up for a mailing list that interests you, but you're afraid spammers might get your address. We'll call the list "exoticflowers". Sign up with the list using the address "[email protected]". Email to that address will still come to your "[email protected]" address even though the "To:" will include that "+exoticflowers" in it.
Then set up Gmail filters to shuttle that +exoticflowers email past the inbox to a specific label. Neat. Thanks, Steve!
Sorting your email with GMail [Personal Made Public]