It's a UNIX box, man.  The most
(programmer-)friendly OS in
 existence.  At least for even moderately technical people. 
 There are
UNIX-compatible people and non-UNIX-compatible people (cf
 Unix Hater's Handbook). 
 
 Even aside from that, I'm not convinced.  I think Symbolics Genera is
 arguably more programmer-friendly, though that could just be because I
 find Lisp a much nicer language than C.  (There may be even better
 OSes; that's just what I have personal experience with.) 
 
I find programming under batch-mode OS to be more pleasurable.
Peace...  Sridhar