I started the thread so I am happy to post my experiences and answer the questions that have been posted.
First - I appreciate the Char (and Daylily) letting us try this.
I traded daylilies for daylilies; daylilies for other perennials (peonies, TB iris and some others) and ended up selling a few fans of a plant that I was dividing anyway. I am very happy with my trades (and I hope those on the other end were as well!)
For the trades that were plants for plants, yes, we just paid postage for the individual boxes. We went back and forth a few times via tree mail to pin down the details but it all seemed to go relatively smoothly and ultimately (I hope) worked out in everyones favor). Personally, I have a lot of plants that I love and may not have every ordered because early on people were kind and generous so I tried to approach this with the same mindset - I was shipping boxes with things I generally would have shipped to my mother. In fact, she got the leftovers from a couple clumps.
With regard to Spring, I would likely be willing to participate but the timing is a little harder to pin down. March is typically too early but the very end of March or early April would probably work. At least in this neck of the woods.