Though this hack in Gmail has been known for a while, I read about it today and found it interesting enough to share it. As Amit decribes in his post, GMAIL lets you create unlimited number of aliases for your gmail id and you can then give these aliases on other websites without worrying about spams. The trick is to use '+' addressing!
As he says, gmail ignores anything between '+' and '@' in the email address. So a mail sent to firstname.lastname@example.org or email@example.com will all go to firstname.lastname@example.org. In the received mail, "To" will still point to the original id to which it was sent which makes it easy to create spam filters based on the 'To' address. If used intelligently, you also get to know which site leaks your address and creates SPAM. So, if I have to give my mail id to any website xyz.com, I can give 'email@example.com'. If I get the spam with 'to' address as firstname.lastname@example.org, I get to know that its xyz.com that had leaked the id and creates spam. Pretty cool..