A new ROM is now available on their site, and offers the following fixes:
This software is suitable for the following devices : HTC Touch Diamond
HTC Touch Diamond ROM update
Release Date: 2009-01-16
An updated ROM is now available for HTC Touch Diamond users to download. As always, HTC is committed to providing customers with the best possible mobile experience.
1. When you launch the Camera while the system is working on other programs, the preview screen may become black.
2. When playing a video, sometimes a portion of the video will be cut off a little bit.
3. Fixes Audio playback problem with the speaker. Specific issues: sometimes the music will turn off and on after 10 minutes, or there is a buzzing sound or no sound at all.
4. Fixes the problem of not being able to receive MMS when in standby mode.
5. When launching music via the Music tab on TouchFLO 3D, the sound may intermittently turn off for a second and come back on.
All in all the update seems pretty minor (compared the the leaked Sprint Diamond ROM for example), but who knows what other goodies HTC hid in there.