Obie Fernandez posted an interesting set of criteria regarding an hypothetical position of Ruby on Rails developer.

There were merely any advanced technical requirements (except a 3+ months experience dealing with RoR, compare that to the usual 5+ years Java EE experience [*] requirement and you get an idea of the learning curve) but in addition to a strong sense of design ("presentation is everything") Obie would require any candidate to run a blog.

This is one of the smartest job applicant filter I've seen for a while (since the "google me" filter actually). If you meet this requirement, it means that you've got the habit to produce written material and that you're passionate enough about something to have a word to say about it. Those are two great, if not the most important, qualities of good programmers.

Blogs are a wonderful screening and profiling tool for employers, partners, clients and colleagues. Your archives have probably much more to say than demonstrating your prediction skills...

All the really great programmers I've met had a real passion for the code or at least a cause to program for. This makes a huge difference in quality and productivity if you compare the work of this kind of person with the average IT slave who's in it for the check...

[*] Most of the time those X years actually means, X times 1 year spent rebuilding the same kind of indutrial-strength highly scalable enterprise bloatware with Struts. Just kidding guys!