Oh brother, I know your pain. I too have a 6 character gmail address because I signed up in 2004 when it was in beta and I too get email for all sorts of people (both accidentally and because people just give out my email address as a fake when they sign up for something stupid).

It can be fun too though, like when someone signs up for a dating site with your email and you can login to what is effectively your account.

I had the same problem as you with a large bank... kept getting emails with someone else's balance in them. I kept responding and trying to get the bank's attention, but nothing. Eventually I tweeted at them publicly with a description of the problem and that got them to clear it up pretty quickly. ;)