If everybody and his brother starts using it for TV connections there is a good chance you will start seeing users overlap on another , especially in higher density housing areas like apartment buildings, townhouse complexes or even just urban and suburnan areas where homes are close together (typical property sizes an Long Island are in the area of 60' x 100' plots)
60' X 100'???!!! Wow... the benefits of living in somewhat rural NC...
As far as congestion... some 802.11n models operate in the already congested 2.4GHz spectrum... so you're right... big issue there. Although 802.11n can also operate in the 5GHz range where congestion is not nearly as big of an issue.
It all depends on the implementation... which if memory serves me correctly... 802.11n is still draft status... there's always the unknown... something could change.
Dave