HTC have pushed out a reasonably significant firmware update for the HD2, addressing in-call voice quality as well as tweaking accelerometer performance. The update apparently improves automatic portrait/landscape orientation flips in the preinstalled Opera browser, together with offering what sounds like gapless music playback from the HD2's mediaplayer.
Update: Antony points out that this update has been around for a while - Thanks! However HTC have also pulled the recent SMS update for the HD2, which users had mixed results with. No word from the company as to their reasons for doing so.