I use GMail a lot. I love it. One thing that I really love is the fact that you can create spam-resistant e-mail addresses like by adding a + sign after the user part.
So, if your e-mail address is example@gmail.com, and you have phone service from AT&T, you could give the AT&T website this address: example+att@gmail.com. This way, if the evil overlords in the AT&T marketing department ever sell or otherwise leak your address to undesirables, you can simply redirect all mail to the special AT&T address to spam and never have to worry about it again. Besides, it adds an audit trail, so you can easily trace the leak to its source.
The problem is that waaaaay too many websites think that the + sign is an invalid character in an e-mail address. This is not true. So, if you are a website owner with a broken site, please fix your validation checks!
[Incidentally, at&t is used only as an example here; I'm not complaining about them.]