I think applications like this started when RIM decided to include the camera and other user friendly items.
The line has been blurring between business usage and personal time as people are now working all kinds of hours, always connected etc .. so me being an admin - I don't want to dictate what can or cannot be used on a mobile device as I see both sides being an admin as well a user.
Anytime I'm asked to modify the BES policy - e.g more restrictive I ask how to respond to push back and state I will not govern a "because you know X or your above X so this doesn't apply to you" way of administrating. I feel the more you restrict the less appeal it will be to use a device. So you have to weigh all this and decide. I feel the personal productivity gained by having a "connected" workforce outweighs locking down all personal fun a user could have.
Now .. there is another side of this where a user would be outright putting the company at fault and using a company provided technology to engage in stated bad activites so the facebook app is interesting that will have to be watched. Possible make a software config that black lists it. For now I'll play dumb as I have enough projects on my plate