Some more enhancements in OS v4.2.1.106 that I have stumbled upon (don't believe that these have been mentioned previously):

1. Bluetooth DUN now supported (slower than USB due to Bluetooth limitations);
2. Bluetooth transfer (send/receive) of media files (e.g., ringtones, pictures, etc.) now supported;
3. confirm delivery, confirm read, and send read receipts now supported for BIS accounts (configurable per BIS account);
4. e-mail and SMS messages can optionally be configured to separate inboxes (options of Separate, Theme Controlled, or Combined); and
5. calendar/task notifications now consistently work correctly in a BES environment (previously with OS v4.1, I would periodically only receive sound/vibration with no event info on the display -- "fix" would be to delete all events from the device, and re-sync, but it was only temporary).

I am sure that there are many more!