I read about a test once where a group in
Las Vegas wanted to see how far they could make off the shelf wifi
gear reach. One team set up on one of the mountains around Las
Vegas. The other on a mountain in Utah over 100 miles away. They
used 12 foot satellite dishes as the reflectors.
Those are indeed ad hoc hp machines and a number of people
don't even know they are even broadcasting. I have noticed it
most with hp. And it can be suprusing how far they will reach...