I joined the Society of Children's Book Writers and Illustrators earlier this year. There were several reasons for this. Many authors said it was helpful, a few agents listed it as a requirement for submission, and this seemed to be the only organization that was consistently, across-the-board, considered to be a mark of professionalism in writing.
I've got mixed reviews since joining though. Some of the printed information is brilliant...some of it seems rather obvious or inapplicable to me. I can take that with a grain of salt--if you're trying to please everyone, there's got to be compromise. It just seems to me to be a little over salted by this point. The website design is great! ...but there's hardly ever any good new information that I can find. There's a message board for writers across the nation! ...but no one's on it (look at the log dates--there's months between posts in threads). The state chapter seems very active! ...but not in my area (the active part is a 4 hour drive for me, from the mountains to the center of the state).
So at this point, I'm still in the trial stage of SCBWI. I'm considering a national workshop, maybe next year, when I'm more ready to present my novel. I'm hoping that there will be more local stuff for me, or at least something within a 2 hour drive. If nothing else, the publications have kept me up to date on the publishing world, and it's always good to be a part of a professional organization.
Besides which, I have to consider my position--I live in a rural area, so I have to expect to drive to others to get what I need.