Spam
I've tried the test recommended above, that being make new hotmail addresses, and never use them to see if they get spam.. and they end up getting huge amounts of spam. Eventually I got sick of hotmail dropping my account after 30 days and switched my main email to Gmail, and then I created a spam account for gmail as well. So anywhere I sign up gets the spam account (which I have forwarded to my main account). I never get a drop of spam email in my inbox. Not a drop. In the past 2 or so years I've used gmail I've had 1 or 2 legit emails get dropped into spam, and those were me signing up to a forum or what not. This email address gets plastered all over the net, but gmail manages to catch the spam from it. Morale of the story? It's not how well you guard your email address, it's how crappy hotmails spam filter is.