Similar to the idea of using you CPAN id, you could also use your company name as the root of your namespace. Most of companies I have worked for in the past five years have done that, and it works fairly well.

Obviously if you work for a massive corporation you many find that your have replaced clashes at the root of the namespace with clashes at the next level down, where your version of <company>::Math conflicts with another team half a continet away.

The other issue would be if you work for an internet company where the public are creating both authorised an un-authorised API interfaces to your publicly facing systems, so if you work for Google, then it would probably not be a good idea to use that as a namespace root, and you will conflict with other people creating Google APIs.