rom gizmodo.com:

If you want to stream 1080p TV shows and movies from the Zune/video store this fall, your 360 needs to be hard wired to your router, or on an 802.11n network. Knowing this, Microsoft is readying an official 802.11n adapter.

But anyway, an official 802.11n adapter for the 360? Sounds good to me. It's hit the FCC, and we'll let you know pricing/availability when Microsoft fills us in.