My experience with Encryption is that it needs to be all or nothing. If you leave the user the option to not Encrypt data, then they won't.
I spent the last year evaluating Encryption software and it highlighted a lot of practices that need managing from a business level, rather than software level, if that makes sense?
Various questions were raised along the lines of:
What data is being taken off site?
Why is this data being taken off site?
Does it really need to be taken off site?
What controls are in place to stop data being taken off site?
As LosOjos mentioned, some users use email as a means of transporting data off site. It's all good and well encrypting laptops and USB sticks, and locking the system down to only allow authorised USB drives to access the network, but if a user can simply attach a file to an email, then it undermines the system.
Encryption needs to be seen as good practice and promoted from the Head/Business manager, rather than a new annoying hindrance that the I.T department has introduced.
I appreciate this isn't quite what the OP is asking for, but I believe it is useful information to share.