Rogue Ameoba's got a legit complaint with the Dock in Leopard: it looks horrible sitting on the side. Personally, it's not really a concern for me, because I've never moved my Dock from the bottom of the screen (seems weird to have it on the side, like the workspace is off balance). But they're exactly right-- Leopard's "perspective Dock" just looks strange in the vertical. The icons seem to float in space, and the whole perspective looks weird.
Of course, they have other problems with the Dock as well-- the reflections of the Desktop and the Windows happen in Leopard no matter where the Dock is, right? But yeah the angles that normally look like a shelf for the icons to sit on when the Dock is on the bottom of the screen look literally "off the wall" when the Dock is on the side.
With something like Cleardock, this is easily fixed. And we're still looking at a dev build of Leopard, so maybe Apple has a trick up its sleeve to fix it before release. But would you put the Dock on the side of your screen if it looked like this?