There's a great piece here on Five common mistakes that Linux IT managers make which is more than just the usual top five mistakes.
To summarize the top five, they are listed as:
- Reactive, not Proactive
- Failing to emphasize documentation and training
- Failing to assess strengths and weaknesses
- Too much, too quickly
- Security as a secondary priority
On the whole there is nothing here that should surprise most managers; how this article differs is that it relates many of the issues back to the Linux/Open Source community and the issues faced by managers and their organizations.