I think I've mentioned DesktopX here before. I'm not using it (yet), but it's very very cool. Maybe now that it's 1.0 I'll have the guts to use it. It's sad OS X doesn't have anything at the system level that is analogous to COM or OpenDoc, because even if Stardock WANTED to port to OS X, they'd have to build a component interface on top of (or under) their product.
Actually, I hope they do it! :-)
I've been a Stardock customer since, oh, 1995? Day 1, anyway. I bought their first product and probably the majority of the products they've ever released. Object Desktop (ControlCenter in particular) totally rocks. It's been on every PC desktop (OS/2 or Windows) I've used (home and work) regularly since I first saw it.