http://www.microsoft.com/downloads/details.aspx?familyid=4c254e3f-79d5-4012-8793-d2d180a42dfa&displaylang=en

New features include:
• New partnership wizard to help customers more easily setup a sync partnership
• Faster transfer of data files including media
• Ability to sync photos assigned to contacts from Outlook on the desktop

ActiveSync 4.1 supports PC sync via USB cable, Bluetooth, or infrared connection.

NOTE:
Faster file transfer speed and photo sync via Outlook are only available for Windows Mobile 5.0-based devices.

Remote PC Sync (via Wifi or LAN) has been removed due to Enterprise customer feedback around security issues. If you are using this feature on a Windows Mobile 2003-based device, please continue using ActiveSync 3.x or earlier.

Beginning in 2006, customers using Microsoft Exchange 2003 Service Pack 2 with devices running the Messaging and Security Feature Pack for Windows Mobile 5.0 will benefit from the following feature enhancements in ActiveSync 4.1: DirectPush Mail, local device wipe, and certificate-based authentication to Exchange Server.