I've written six or seven WIPs, and I always, always regret posting them in chunks, because two thirds of the comments will be "update soon" and "moar please!" Sometimes I just wanted to hear specific feedback on that chapter, and boohoo, it didn't happen. I don't really write WIPs anymore.

I generally posted once a week when I had the entire thing written, or once every couple weeks when I was in the process of writing it. My chapters were usually 3000+ words, so a couple weeks gave me enough time to write them and get them beta'd.