I have participated in themed block swaps and have had very positive experiences. I have loved most of the blocks I got back and appreciate all participants and the hostess. I always do my best to double check the fabrics I send to make sure they are name brand fabrics that would come from a LQS. I have an Accuquilt so the blocks will be 6 1/2" unless I have a problem lining them up on the Accuquilt and have to cut them down to 6". That is within the rules 6" to 7" usually.
I think I would like the kind of swap where you send around an envelope stuffed full, take what you want, replace, and send on. That does sound like fun.
I haven't done any swaps where I would put together a quilt or handmade item for someone else. I just don't feel confident enough yet for that.