It’s as big of a risk as your organization (management) is willing to let it be.
The reality is whether or not you tell people that they can use their own mobile devices on the network, for corporate email, information storage, etc., they’re going to find a way to do it anyway. Why not set everyone up for success and create a formal BYOD program that supports the major platforms, gives you and your IT colleagues the visibility and control needed to keep things in check, and be done with it?
BlackBerry is one of the most recent splashes into the BYOD/MDM market with Mobile Fusion (good stuff worth checking out) but there are plenty of other solutions. Here’s a short video with some more of my thoughts on BYOD and here are links to other pieces I’ve written about mobile being the new desktop.