I find my Treo slippery and am always concerned about dropping it. Moroever, I like to put it in my shirt pocket when I'm sitting down, which is a recipe for a dropped unit and broken screen.

I found Scotch brand Fabric Cubicle Grips at the container store. Big office supply stores should have these, too. They are for sticking things to cubicle walls. A couple of squares on the sides and back make the treo much less slippery. A good aspect of this solution is that the grips come off without leaving residue on the Treo. I don't know, though, how long they will stay nice.