I do something similar. If I sign up at Slashdot, I'll use the email address slashdot-SECRETKEY@domain.com, and if I sign up at Gawker, I'll use gawker-SECRETKEY@domain.com. Those emails get forwarded to my real email account.

Nice thing about this system is that I can immediately tell where spammers got my email address and shut it off. Also, any email that comes in that doesn't contain a SECRETKEY gets ignored, so I don't have to worry about spammers sending to sales@domain.com and admin@domain.com.