IT support works best when they maintain core systems adhering to open standards. That way they can supply mainstream users with standard devices/environments, while still allowing sophisticated users to connect and get their work done. Part of the deal can be that sophisticated users provide their own support for their environments.
For example, while secretaries may be best served by running Windows, it often makes good business sense for dev teams to work on their target environment. A good dev team won't have any problem supporting themselves so long as the infrastructure is solid.
A special class of user is the early adopter. Befriend these people because they are investing time in experimenting with new tech, some of which will become mainstream (and some of which is passing fad). So long as you insist on them supporting their own crazy experiments, their efforts are a net win. For instance, early adopters seem to have worked out that iPads will be the mainstream winner out of the tablet field. That's a whole lot of research and evaluation that IT doesn't have to do.
What about security? I think this is often used as an excuse for trying to (quixotically) maintain some kind of status quo. Of course security is important. Appropriate policies should be enforce by core systems, with the assumption that pretty much all mobile devices are insecure. For instance, there's usually no need for a lawyer's iPad to access the central source code repository, and this is trivial to enforce without descending into a subjective argument about which mobile devices are less secure. They all suck.
The big picture is that the way we live and work is changing. People carry lots of powerful mobile devices, and work and leisure are ever more intertwined. Good IT people will work out a way to support their customers. The rest will go the way of the mainframe operator.