Mike: Everything is traceable... its just how far you're willing to dig to get to the piece of sh*t that keeps most people from trying.

Even if they sign up with a free yahoo or msn account, they keep records of where they signed up from. Typically from an anonymizer proxy. Thing is those proxies are meant for people in countries like Iran and China to get to sites that would normally be blocked by their governments, and NOT for spammers. So when you emailed the anonymizer people, they just might give you the non-anonymized IP address, which you can take to the appropriate ISP.