Well, I'm half way through Julie Hedlund's 12 x 12 picture book challenge, and absolutely loving it!
The challenge is to write twelve picture book drafts, one a month (and there's the extra challenge of aiming to revise a manuscript each month too).
There's three levels of membership, depending on what stage you're up to in your writing career. There's a forum where writers can discuss craft, and other topics, and a Facebook page. Each month there are posts from guest writers/illustrators, and a seminar from an industry expert. (I've learned some real nuggets of picture book wisdom from these seminars).
Probably the best part of it, is the community and support of other writers ... 650 odd of them. If you ever feel like you're on your own out there ... you're not.
For me, the best things about 12 x 12 are:
So far, this year I've drafted seven new picture book manuscripts. Hooray! (I'm not saying they're good, in fact a couple are seriously bad, and the others need some work ... but, hey, that's what writing's all about, isn't it?)