Miniver has some interesting points about how the Advogato certification system is measuring 2 dimensions with one measurement: programming ability/knowledge and open source experience/contributions.

I'm one of those people who thinks that open source is a great idea, but much of my professional career has been spent working on proprietary software. I've used open source tools, and I think once or twice I made some changes to them, but it was a long time ago.

I've tried half-heartedly a few times to persuade employers or clients to open source some of the projects I've worked on, but usually the code was written in such a rush that I wasn't all that eager to expose it to strangers anyway.