[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