Well, what if you could use a temporary, disposable email address instead of your regular one for such purposes? spamgourmet may be just what you're looking for. I haven't tried it yet but had I known about it before I decided to send a birthday e-card to my cousin in Florida on February 19 via MyPassionup, I wouldn't now have 1294 (and counting...) junk offers from all sorts of companies, clogging up my Gmail account. Luckily, Gmail recognizes most of them as spam. But a few still occasionally get through to my inbox.
I used to be able to brag that my Gmail account hardly ever got spammed. Since February 19, I can't say that anymore.
