Although we develop software for UNIX and Microsoft's various Windows platforms, we use Linux for all our infrastructure and we're not surprised that a growing number of organisations are doing the same.
There are several reasons that we use Linux :
It's robust
It's free
It doesn't tie us into a single supplier
The single major reason we use Linux, however, is that we have access to the source code. This means that if it breaks we can fix it ourselves. Users who don't have the technical skills to do this know that if something goes wrong then support will be available. In our view this is the single most important benefit of Open Source software.
We write systems and application software for both Microsoft Windows and Linux. Of coures, we support the software we write whatever the platform, but we can actually support the operating system and its utilities if our client uses Linux. This means that problems can be researched and fixed very quickly (often overnight).