I am beta testing OS X 10.5. On a 8 core Mac Pro with 5GB RAM
Good News Unity 2.0 seems quite stable 
The only issue I have found so far is for some reason I cannot open the Island demo? Unity will crash every time?
Great Work Guys !
Please send a bug report to us using the Report Bug utility. This will include detailed information on the crash, allowing us to see what’s going on.
Yeah, it seems that Unity is unstable on some builds of Leopard on some hardware configurations in some situations. And stable in many cases.
Good thing we now have a couple of weeks to work on this before Leopard comes out (if the rumors can be trusted 
)
d.