For me it is the fact that the system seems to have multiple personality disorder. There is a unix system in there and a Mac system in there, the two are not w

For me it is the fact that the system seems to have multiple personality disorder. There is a unix system in there and a Mac system in there, the two are not well integrated. There were a number of times I would do something in bash and not be able to find it in finder. It has been a while since I used it but at the time smp support was quite poor. Running a build that would max out one processor of a dual processor box would cause the system become unusable, as it tried to load balance the one job between the processors. Sadly in my experience so far, Win7 has been more stable than OS X.