This remote is exactly the same as any other Harmony remote, except that it has the red, blue, yellow and green buttons.
Yes, you can use the remote to browse through the marketplace and with the HD-DVD player.
I have a Harmony 880, and it works with the 360 perfectly.
I guess what I am saying is that a Harmony remote can do so much more than just operate an XBox. So the best remote to get would be the one that has the buttons that work the best with your entire system (DVR, DVD player, XBox, etc...). The hard buttons and the screen size and quality are really the only differences between the different Harmony remotes.
For instance, I really like the 880 because it has the transport buttons right in the center of the remote, where it is easy to access them. Some of the Harmonies have them at the bottom, where the thumb-reach is a pain.
Josh - GamerTag: ShapeGSX PSN: ShapeGSX
'97 Eclipse GSX - email@example.com in the 1/4