I used to think that a programmer's tools are sacred and you should basically let people use whatever they feel they are most productive with, but I'm starting to see problems with that, at least in big organizations..

First, IDEs - I've worked on teams where 3 different IDEs were being used by different members of the team - IntelliJ, NetBeans, and Eclipse. It worked fairly well and no real problems came about as a result of the different IDEs. I've also been in training sessions where everyone is using the same IDE except for some crackhead insisting that their IDE is better and that they can't switch to Eclipse even just for the training, and everyone in training has to wait for half an hour why the instructors try to help them figure out why stuff isn't working in their IDE.

Second, platforms/libraries/frameworks - There are really a lot of valid reasons for standardizing the platforms, libraries, and frameworks your organization uses. You have better internal support, can leverage work done by other groups, and training is easier. Being able to switch people around easily is perfectly valid as well - people leave, get promoted, need a break from their project, want to explore different career goals, etc.. Plus, I think it is good to send people off to other projects to learn and share good practices. Having a standard set of tools makes this relatively easy - all you really need to learn on a new project is the business side of things.

That said, there isn't a one-size-fits-all solution, so it probably makes the most sense to pick a standard set of tools for common project types. If a project needs to deviate from one of those standards, that is fine, but they need to make their case for doing so.

So for full-blown enterprise apps, the standard may be Java EE. For smaller apps, it might be Rails or Grails. For desktop apps, you might mandate .NET. Then if someone says "Hey, it would be cool if we wrote this small app in Python", then they could do it, but they would have to show that the benefits gained by using Python in that scenario would outweigh the costs of using a non-standard platform.