How can I stop someone else from using my email address?

Dylan is getting account sign-ups from someone with the same name, who is mistakenly using Dylan's email address. What can he do?

I subscribed to Apple's MobileMe service, so I received an email address with my full name @me.com. When the service switched to iCloud, I also received the @icloud.com suffix.

My problem is that someone with the same name, based in America, is using my @icloud.com address to sign up for accounts and services, including Instagram. For example, I know that he has purchased a case for his iPhone 4, is interested in a new Ford pickup truck, and has signed his child up for a Scholastic education account.

I get this as well. A surprising number of people don't seem to be able to remember their email addresses. This is a growing problem because of the use of real names. We used to think this was a great idea, overlooking the fact that there are often hundreds and sometimes thousands of people with the same name, and now they're all coming online. We might have been better off using fabricated but memorable names.