Anyhow, the C++ API of BeOS was amazing. OSX/Objective-C still don't give you that OO access to the OS feel that BeOS had. My one major gripe with their approach was in the way that they managed run-time binding -- it was very brittle from release to release of the OS. As a developer, you had to ship separate binaries for each OS release you wanted to support. Nasty.
I'd love to see Haiku take off and become a viable platform. If for no other reason, just to have a reference version of how things CAN BE DONE.
That cheerleading aside, I have to say that with a fresh OS install, my OSX Lion 2009 PB performs great. Very snappy, runs cool, starts up quickly. It's only when you start installing all your apps, VMs, widgets, drivers, and misc. junk that it slows down. Would Haiku do any better if it had that rich of a software environment?