Recently we've been interviewing candidates for jobs at Blue Fountain. We are looking for developers and sys. admins willing to do some work on our stuff. Nearly all of our systems are open source, so naturally we are looking for open source developers. Naturally everyone we chat to is very enthusiastic about open source and keen to work in a company that uses it.
And the conversation goes like this (with one notable exception):
Me: are you involved in any open source projects?
Interviewee: not really, what do you mean?
Me: have you contributed code to any open source project?
Me: are you on any mailing lists?
Me: do you have any open source code I can look at?
Me: do you have a blog?
Me: ok, let's move on
To me real involvement in a open source project indicates a keen developer one step above everyone else.