On the debian based OS’s (Raspbmc / Raspbian), if you run the device headless most of the time you can ensure the HDMI port is powered off by editing /etc/rc.local and adding the below line above exit 0:

/opt/vc/bin/tvservice -o

(notice its the same line that I posted in the script to turn XBMC off and on in Raspbmc).

Reboot and done. Not sure how much you gain from this but its a nice little trick.