Use of OS X in HPC and scientific computing is low and it has to do a lot with the pros and cons of OS X w.r.t. the alternative (Linux)
OS X Pros:
* Polished UI; still *nix
* Desktop/Design app(s) such as MS Office, Adobe programs well supported
* Multimedia very well supported
* Some people like the Apple ecosystem (iPhone, iTunes etc.)
OS X Cons:
* Runs on expensive hardware and not everyone likes Macbooks, specially people used to Thinkpads (keyboard+trackpoint)
* Cannot upgrade hardware (e.g. if you want to try the latest NVIDIA card with your CUDA app) on desktop/cluster
* Bloated GUI that cannot be customized (in Linux you can use a minimalist window manager)
* Package mgmt in Macports/Fink is sub par compared to Linux (Debian) distributions. 81
Most packages are not even actively maintained or are orphaned
* Some useful tools/programs traditionally did not run or still dont run on OS X. For example ...
* Sun Studio still doesnt work
* Valgrind only started working recently and not all features are supported
* Intel compilers have also been available in recent years
* Apple doesnt even package a Fortran compiler and you have to rely on 3rd party (mostly individuals) to build binaries that work only on certain OS X versions (which the individual has). Support is rare or non-existant in such cases
* Commericial scientific apps (ABAQUS, ANSYS, FLUENT and many more in industries such as oil/finance/engg etc.) do not run (natively) on OS X
Linux (Debian) Pros:
* First class package management i.e., installation of compilers, most numerical/scientific libraries etc. is a command away
* Unlike Fink/Macports the packages are much better supported (in Debian you have the option of using bleeding edge/testing/stable versions)
* Most cluster(s) run some version of Debian/Red Hat so less hassle in porting code(s)
Linux (Debian) Cons:
* No standard UI
* Linux on desktop/laptop(s) may require some tweaking to get everything (suspend/resume, 3D video acceleration, sound etc.) working but this has improved a lot in recent years
Baring some exceptions most users and cluster/system administrators find OS X easier for desktop productivity and NOT for scientific computing (compiling, using, developing stuff).
OTOH most Linux users find the latter easier than former and this is reflected int the entire HPC/scientific computing ecosystem. 81