Basically, someone else on the internet is trying to access various accounts under my name and registering new ones with my email address. From the information I can glean, it seems likely that the other person has forgotten their real email address and thinks that my address belongs to them. They keep having "password reset" emails sent to my account, and at one site has gotten customer support to issue a new password (fortunately, the ticket went to my inbox and I have changed it back).
Unfortunately, I can't contact him/her as he/she is using my email address to sign up for things... so far it's only two accounts, but I would really like to find some way to make it stop before all my passwords get reset. Has anyone encountered this kind of problem before/can think of some creative solution?