This isn't really a category suggestion, but a suggestion for the board itself. I think it would be fun to have like a monthly contest or craft challenge to get everyone involved. Each month could have a theme. People could post pictures of their project and a winner could be selected. The prize could be like a soap or craft supply gift certificate or something.
I do have a category suggestion as well though: maybe a separate forum for recipes. I was looking through the soap forum to see what recipes i could find and I thought it might be better (especially as the forum grows) to keep them somewhere specific.