One thing to note over XBMC, is that as a "for profit" company, Boxee has been partenering with companies like Iomega and D-Link to release it's software on stand alone and integrated hardware platforms. The Wikipedia entry for boxee states that the folks at Boxee would love to be OEM'd into Televisions and bundled with other set top hardware.
Boxee is avaialble as a download to be run on MAC, Linux and Windows. You can check it out at http://www.boxee.tv/
A really great write-up of the boxee box can be found here:
Also, Mike has a really in depth review of the Boxee Box product on Amazon's website. Scroll to the bottom:
I look forward to exploring my boxee more and expect more features to be added as updates become avaialble.