My experience with swaps has been like you describe. Generally you sign up, we had to commit to 6 blocks, they all got sent to the organizer. She then mixed all the blocks together and sent out the blocks. When we sent them to her we had to include a large envelope and postage so she could send them back to us. I'm sorry to say I was not happy with my blocks. Some of them were not square, some were smaller than the specified size, points and seams didn't match up. After I cut them all to the same size, riped out and restitched a few I was able to make something with them. Another thing to consider is color and prints. Some swaps specify what to use and some specify no batiks.