Some of the things I have read about it is that it doesn't support any version of exchange save for the NEW version that hasn't been released as of yet.

Plus older versions on SQL Server will not run on it either, only the current edition will run.
I don't know if this is security related or if its simply a way to force consumers to upgrade.

I like Windows as my desktop , but I say "No Thank You" on M$ Servers and will be sticking with linux/BSD for my serving needs. (Both security wise and expense wise)

--Just my 2cents