You can never be 100% bulletproof, but you don't want to open up more holes in your security because a user wants to play Angry Birds on their phone.
A smart phone is for calls, emails, and texting.
I love it when a user says they "need" an iPhone or Android phone to be more productive.
Yet when I press them on HOW this would make them more productive, they stammer and can't come up with one reason.
Coolness, comfort, and "because everyone else has one" are not valid reasons to add more avenues for breaches and data loss.

That's the reason people don't like the IT Security department, but we do know what's best for the security of the company.
It's our job to know, not a so-called computer expert working in accounting or engineering...