A couple of items to consider. Does Linux support ALL the applications the programmers need to interact with other people in the company? The answer is "no" in my workplace.
Our company has a lot of legacy VBA code that would need to be replaced. Don't get me wrong, I think it would be smart to replace this. I hated the way VBA changed on every release and broke my code base. The last straw was when I needed to access spreadsheets that used 3rd party VBA modules that were locked. I ported my whole back-end data analysis/report generation code base to Open Source R/Sweave/LaTeX. But I'm just one user and did it myself as a spare time activity.
I still think Visual Studio is a pretty nice development environment for C++. I'm trying to get up to speed with Eclipse. I do prefer Open Source. Now that our corporate budget is REALLY tight, that is a big help. Guess the IT folks think it would cost more to switch than pay the annual tribute to Redmond