I won't do tech interviews either, but not because I think I will fail at them. I think they are completely bogus and give totally the wrong signal. It's a waste of my time AND the company's time. I wrote up my thoughts on this exact thing a few months back: http://blog.getify.com/technical-interviews-suck/

TL;DR: Everything you need to know about if I'm a good fit is available online in my OSS (et al) track-records. If that's not good enough for you, that's not the kind of job I want anyway. I want to work for companies that value the full lifecycle of OSS work, which you can only see in such a way, and CANNOT judge via tech interviews.

By the time I walk in the door for an in-person interview, I expect you to already know that I am fully qualified (tech and otherwise), and you're looking now to judge my cultural fit by sitting me down in a real team meeting and seeing how it works, etc.

If I show up and you try to quiz my tech skills, you didn't do your homework on me, and I have no more time for you, so I'll just chuckle and walk out. Politely of course.