I once posted a response to a "what video game are you playing?" topic on some other site. For like five years now I've been getting emails to alert me every time there's a new post in that topic, even though that was the only time I ever visited that site.
I only notice because I recently switched email programs so now I've got to teach it what spam is all over again.
It's weird when stuff like that happens, I had a site I signed up to 10 years ago email me recently only to get shut down shortly after. Also digg has started sending out emails probably because it's been pretty stagnant for a few years.