Even though I haven't posted in a while, I am creating in the mist of life events. The Yahoo! Group: ATC_Fun, has these swaps as one on one's, in which the artist creates an ATC and decorates an envelope(does not have to match). The participant gets two pieces of art for the price of one.
These ATC Mingles are themed. I have participated in almost all of them. I am currently working on an 'Under the Sea' ATC Mingle as well!