||Updating this thread...
1. Open source activity, however little, does help the chance of getting interviewed, getting an offer, and increase bargaining power, even when most of my work experience is not IT related.
2. Many vacancies requirements are over demanding. At the end, they don't really need all that stuff at work. So don't be afraid to apply if you only miss 1 or 2 skills.
3. The best interviews by HR is the one where (s)he is accompanied by a technical interviewer. That is indeed strange.. maybe it's just a common practice in my country. This is actually the first time I actively looking for a programming job.. Anyway, companies where HR interviews by him/herself is usually a company where the programmers doesn't look too happy.
4. Their standard of "good programmer" is surprisingly low, especially for topcoders. Don't be afraid of those technical quizzes. Do it slowly, while sounding your line of thoughts, and achieve accuracy instead of speed since you will probably be faster than most candidates.
5. Getting a decent part time programming job is very tough. You probably better off contracting yourself.
6. And yeah, you don't really have the opportunity to test your interviewer unless the interviewers really open themselves. Once, I blew an interview by risking myself by asking him to tell me an example of his open source work, if any. Note to self, don't ask such question unless you're really sure the interviewer doesn't have confidence crisis.
I hope this information can help others. I'll add more if I remember some more.