Over the years the hardest thing to find is someone who understands the Darwin (which is Unix right) and Mac.
I mean we have a rack of Mac OS X servers which have all these cool Unix and open source tools in them, like Cyrus, that should be doing cool stuff for us.
The Apple gui's are but do fall short at times, if you can find unix or linux guy they can't help you extend that without starting from scratch, the Apple certified guys don't go beyond the gui normally as most have no training in whats going on below.
So after that rant, advice study the general.
Anything that will expose you to a range of similar systems is good. Then look at a specific system that grabs your interest to specialize in, hopefully that is still Mac OS X.