In our guild, the BOM is done both for a member raffle for all those that participate and also additional blocks for our charity--disaster quilts for fires, etc and to the local cancer foundation. Our BOM chairs have figured out that most will participate when the block is a quick, easy one that they can use their scrapes on. Since most are working on their own projects and we have almost monthly workshops/classes, members don't want to spend a lot of time on BOM. One year, we had a mystery quilt going with the BOM--you'd make a block for charity or the drawing and then use the same block pattern to make one for ourself--basically a mystery sampler quilt. I would note that everyone wants total yardage needed if you do that.