@Amit: Gmail's + addressing often causes problems in forms wherein the coder has tried to act smart and use some scripting to validate the input. It's a good idea but then they ought to be smart enough to implement the appropriate RFC describing email usernames. (+,-,_ etc. are valid characters).
I much prefer Fastmail.fm's sub-domain addressing.
As an example - assume I have a mailbox/account user@fastmail.fm
I can then create aliases like spammingsite1@user.fastmail.fm
bookmarksite2334@user.fastmail.fm
and so on. Naturally, when you get spam, all you need to do is look at the headers to figure out which site has leaked your details.
Even forms wherein Gmail's + addressing is rejected will support this sub-domain addressing.