A pretty big chunk of our customers use us for this purpose. Any files synced down to a client sit in AES256 containers that have to be mounted on boot/login by the OS. In this way it kind of works like a networked version of TrueCrypt.
When a device is lost/stolen the files can't be accessed without logging into the OS then into the software - they reside in the encrypted container which can't be accessed without logging in.
On top of that, you can remote wipe individual or all devices a user has accessed. If the device where the software resides is online, it happens immediately, otherwise the device phones home when switched on and wipes the encrypted containers.
The product is CloudFileSync and we are Network2Share. You can find more info in the weekly vendor thread or our websites.
Very late to the party here, but I'm working for a developer that produces a 100% channel file sync and share platform called CloudFileSync. The developer is Network2Share.
We have built CloudFileSync for MSPs to solve file sync and share problems for customers who have tricky requirements, or who have lost control of their files via staff use of personal-grade file sharing tools.
CloudFileSync provides secure, auditable file sync and share software that can be hosted anywhere and has been designed primarily for MSPs and their customers, unlike other personal grade solutions who have added the channel as an afterthought.
The goal is to provide the flexibility to solve any tricky project and the security features to do it properly.
Drop me a reply or PM if you want to know more.