Honestly, I never use them. In my opinion, word of mouth goes a long way in the video production world! Also, being near a lot of filmmakers (aka living in a big city) can really help a lot too. The secret to getting work is to be patient and work hard (I can't stress that part enough)! Eventually, if people notice your hard work and creative abilities, someone will refer you to a job that you want. It may start off as only a part time gig but part time gigs can lead to full time gigs if you prove yourself to be indispensable.
I have actually used Craigslist to get some jobs before. However, I still think all the best jobs go to those who have an ear pressed to the floor or who have a friend who trusts them in the film and video industry. You have to be connected!
That's my two cents. Hopefully it either confirms or helps you realize how the crazy video business works!