What Distro is Google using?
Employees have a choice of a MAC (mostly for image designing, movies, and sound) or Linux. Development would highly be a Linux machine for the server applications and the 100% customization of the OS to fit their needs especially for security.
First thought for Linux, DBM or RPM?
Next, KDE or GNOME?
And finally, Intel or AMD? It's not software, but people do have a preference.