Biggest one for me is Netflix metro has hardware decoding and access to 1080p streams. hopefully soon it will do DD/DD+ 5.1 sound passthru as well.
Website is stuck using 720p max and silverlight.
if you are using an ion settop for HTPC or AMD E350, it won't even do 720p because of silverlight (/w DRM) isnt gpu hardware accelerated. lots of dropped frames. Also silverlight will never support 5.1 sound.