I remember installing BeOS when it came out. It was impressive and beautiful, and I really wanted it to catch on. I think I'll give Haiku a spin. With VMware, it'll be much easier this time around.
But the user space and the user interface are brilliant!
I would trade Gnome, KDE, Windows, OS X, or $NAMEIT for the BeOS userland any day, both as an end-user (wrt. UI) and as a developer (user-space API). I hope we'll have more choice in the future.