Think of it like "remote management" for your Smartphones/Pocket PCs. Very Blackberry-like, and little bit SCCM-ish.
Short list of features:
1. Device Management solution that integrates directly into a Windows Server infrastructure
2. Full, Over-The-Air device provisioning
3. Automatic deployment of targeted applications to devices
4. Secure data channel from the device to the corporate network
5. Enablement of core LOB scenarios in a mobile environment unlike before