I ended up buying the Elevator, after thinking a while about it the mstand just seemed something a bit overdesigned. It has already shipped, let's hope I won't regret it.
Well, I just got my Elevator. I must say that I actually like the look, even the plastic piece. The rubber stripes seem to keep the powerbook still, for the moment I don't see how it could ever slip since it seems almost glued. Only thing that annoys a bit is that wobbles (not terribly) even by typing on an external keyboard.
I bought one for my Powerbook 12" and Dell 20" wide at home and loved it so much that I bought one for my work, where I have a Macbook and a 20". I have never had a slip issue, it's very portable which is cool. I take it with me when I shoot weddings and put my laptop on it and use the finder slideshow to fade through pictures of the day. Looks very classy.
It is a little wobbly, but nothing worrysome at all. And having only air around it is perfect for cooling.