If certified Play To devices become common, or DLNA devices start working more reliably with Windows 8, this will all be a fantastic way of streaming content around the house - especially if you buy into the new Xbox music service, which will include free streaming music on Windows 8 when it launches.
Today, it's great if you have an updated Xbox; the screen and speakers that it's connected to are likely to be much better for enjoying music and video on than your laptop or tablet, and your laptop or tablet is a much better way for most people to control an Xbox than a controller designed for gaming.
For older DLNA devices, unless it just works first time, it ends up being a frustrating experience.