I was thinking of trading one day of code against one day from a graphic designer. Is that a trend, bartering for skills? This could be a great way to help each other out.

The way I would make sure the bargain is fair is by basing it on time. That's why I say start with one day. Then it's just a question of how skilled we each are, but worst case, I lost one day to code in exchange for an ugly design. I can live with that.