The MacOS X user interface, `Aqua', is very nicely polished; rendering seems fast and beautiful. But underneath the glitz, it leaves some things to be desired.
Examples related to debugging the system: man pages are not provided for quite everything, and the man pages that are provided are not entirely consistent with the system as sold.
No strace or truss utility is provided.
When Mac programs started with the "open" utility (i.e., gui programs) die, they don't dump core, they don't seem to log anything to the syslog facility, and there's no accessible stderr.
For example: the "Help Viewer" program seems to die any time it's opened from within another program, but I don't know of any way to figure out why it's dying. If it were an X program, I look at its stdout, or strace it to see where it's croaking.
Probably the root cause for this is that it's all relatively new to the Apple folks, and so they're having to work out the bugs. But I'm a tad bit further irritated that Apple doesn't make it easy to contact them in order to suggest that something might be a bug. I may be the only person who's tickled some of the bugs I've run into -- will they ever be fixed? How will Apple ever know that these bugs exist?
A beautiful UI is nice, but I'm not sure that it's worth the hassle of using a poorly-evolved system.