In my opinion Linux OS's are more personal toys than anything else. While they are great for home use, Linux just doesn't fit in to the IT professional world. As an IT manager, I could never see implementing linux into our network for many reasons:

1. Training (most all uses have no idea of what linux even is)
2. Hardward support compared to Windows
3. Range of business applications available
4. Technical Support
5. Scalability
6. Compatibility (ties in with applications available)

While the cost would be a huge benefit, all of the other issues above would counteract that cost AND take up the most limited resource available, time.