Because the demand for Drupal talent exceeds the supply, it's incredibly hard to hire talented Drupal developers. In a recent blog post I advised people to hire good Java or PHP developers, and to get them up to speed on Drupal.
We tried once to create an open-source developer out of a normal developer, but it completely failed. We never tried it again. Truth be told, I had an aversion to it. An open source developer is a self-starter. He's competitive - this is someone that wants to prove that they can do something better than you can. As such, it's a great recruitment/qualification vehicle, because you can see their work before you ever think of hiring them. You can see if they'll work out for the company. We definitely took that approach to hiring.
I believe there is a lot of truth in that. First, developers with impressive resumes don't necessarily grok Open Source software development. Second, having experience with Open Source software development is becoming an increasingly valuable asset on any developer's resume. So let me refine my advise:
Hire good Java or PHP developers that are active in the Open Source community (at large), and get them up to speed on Drupal.
— Dries Buytaert