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.
There are different versions of the ROM for the UK, Greece, Russia, Norway, Germany, Spain, Netherlands, France, Czech Republic, Poland and Italy, all with version numbers kicking off from 1.48.4xx.x. It's obviously worth checking to make sure you're actually running an earlier ROM right now, and make sure to set aside 30 minutes for the update to take place.