If you scoured your Xbox 360 for every new update you could find, you may have found a new setting under the console settings. The "Xbox Companion" setting allows you to, you guessed it, enable a Windows Phone 7 linked to your Gamer Tag to remotely control your Xbox with the aptly named Xbox Companion app that launched yesterday. The app is a free download, by the way.
I checked out the app for myself yesterday on my HTC Trophy, which was connected to the internet via my phone's service provider while my Xbox was connected to a separate network. Setup is instant and a notification appears on your TV to let you know that an Xbox Companion is connected. Despite both my devices being on separate networks, the remote access had little to no noticeable lag.
It basically acts as a controller with a display, where you can see all of the content on your Xbox through your phone and access it much easier. You can also control every aspect of your Xbox like a controller, except for the actual game playing part obviously. There seems to be potential for that though. The app seems like it's in a very early stage and I am definitely looking forward to seeing what Microsoft will eventually do with the technology.