I have been using Boxee for some time now in my home as my primary Media Engine. Many people have been looking for a similar solution and I thought I would share my experience here and provide a place to grab an invite if you are interested. (disclosure: my employer Union Square Ventures has made an investment in Boxee)
I use Boxee because it enables me to have one piece of software for all my owned and streaming media needs. Since Boxee provides a way of easily browsing local media I use it to view videos and listen to music that I own. I also use the streaming functions to watch content that comes in through Hulu, YouTube, CBS, and other sources that I have customized via feeds. That is how I watched AirWolf the other day, one of my favorite shows as a kid.
Personally, I have used a third party hack that enables me to use Boxee on my Apple TV. Note: This is not official.
Below is a video from the team at Boxee:
quick intro to boxee from boxee on Vimeo.
If you are interested in checking out Boxee for yourself, let me know and I will send you an invite.
Full disclosure: I work at Union Square Ventures which has made an investment in Boxee