I found one at the World Market in Cary. There is absolutely no concern with sitting on it. I probably could have jumped on it. It's not the most comfortable thing in the world, though; the padding's probably only just over an inch thick.

I can't say the same for the tray side, though. While the sides of the tray were about 3/4" thick solid wood, the floor of the tray was made of fairly thin plywood, and when I pushed down on it, it deflected noticeably. It seems that there are ribs running underneath it along the short dimension: one at either end and two more spaced evenly. There would be no concern under normal use, and someone leaning heavily or even sitting on it would probably be fine. (Not that anyone would sit on it with the raised sides.) But I'm pretty sure that if I stood on the weakest points, that I would punch through.

Again, with the padded side up, there's no concern at all. And there's no way that normal usage would cause any problems on the tray side. But it's worth noting.