Pentax Users: Pentax Forums has created a Serial Number database so you can record details of your gear for various reasons - "The mission of this database is threefold: first, it will allow users to discern faulty items; second, it will build an overview of production trends; and third, it will establish owner records to deter theft."

I've recorded my information and can vouch that apart from any comments as to quality, problems, etc., my personal details are not visible to others using the database. Looks like it might be a useful tool.