Yupo is an interesting painting surface. I finally tried a couple of things on it with watercolor and I feel like I'm only beginning to understand the way it works. It is definitely different from the traditional cotton cold press watercolor paper. Pros I've discovered so far:

• paint stays bright and saturated (of course, you probably use less water than with cotton cold press)
• the way that the paint mixes on paper creates interesting effects (do see the full size pictures!)
• paint stays wet for much longer than on cotton cold press (or hot press). I guess this could be a disadvantage, too, but it does give you more time to play.
• Yupo does not buckle

Cons:

• Yupo is extremely sensitive to any at all grease. While this can be used to create nice effects in the painting, I was a little disappointed to see my own fingerprints all over the paintings. You do need to be tidy when working on Yupo.
• layering of paint, while still an option, doesn't work quite like it would on cotton paper. The underlying layer tends to smudge and mix with the new one. In the painting of poppies, I wish I didn't do the second layer.

Other observations, which I wasn't sure if they were good or bad yet:

• It's harder to control the paint on Yupo than it is on cotton paper. I am suspecting, though, that it is a matter of practice and habit. A lot of people claim that watercolor is difficult in general, and we know it's not true ;)
• It is relatively easy to scratch the paint away from the surface of the paper. I used this effect in the painting, but I also found myself a little worried later that the painting would get scratched just from handling.