Just want to mention that I don't have internet at home & just use my iPhone to access ATP. I'm not sure how well a spreadsheet will work for people using mobile devices.
When I did the piggy swap last year everyone had their own page with a basic form where they listed what they had to offer. Besides the name of the plant and the variety you could also include seed source (garden or commercial), seed age, number of seeds per packet & number of packets offered.
Another thing people might want to do ahead of time is to go to the plant database and add pictures and/or local reports for any of the seeds they want to offer. That way people will know exactly what they are getting and what it looks/tastes like before they trade.
