[_puk]

Whilst great info, unfortunately most of the sites that one would actually try to use this on don't accept addresses containing a "+" as valid.

Another Google Mail trick is to use periods. Not as useful as the +, but for those sites that don't accept +, one can usually add in a few extra periods to place sites into buckets (multiple adjacent periods don't work).

[e-mail]

[technofiend]

Unfortunately vendor sites such as apple.com don't realize xy@g and x.y@g are equivalent and will let people register both. If you accidentally click approve on the confirmation email then good luck getting Apple to remove the second account. Which is how my wife gets tons of email from Apple about a stranger's iTunes purchases along with other random items.

[donutz]

If you control the email address that the stranger registered to their Apple account, you could initiate a password reset, change the password, then login and change the email address to something that's not yours.

You probably just locked the stranger out of accessing their account though, so you probably shouldn't do this, unless said stranger is signing up for all kinds of services using your email address, in which case maybe they deserve it. :p

[jasonkostempski]

Even if they did accept it, haven't spammers figured out the pattern by now?

[philipov]

I don't think spammers look at individual email addresses. They're interested in 50 million emails, not you. I suspect the number of people using subaddressing is too small to notice. If it became popular enough that even computer illiterate people began using it, that's when it would be noticed.