I have used one just like that made by Cisco. We had a spare one at work, so I brought it home to play on my wireless home network.
Notice that the antenna is a yagi, with a whole mess of elements. That makes it is very directional, with a real narrow "beam". They're basically made for connecting two distant buildings together. Once the buildings are connected, you would use some other omnidirectional antenna for the computers on the distant lan.
When I was playing with it at home, I was trying to see what kind of signal I could get on the other side of the house. The problem was that the beam was so narrow, that there was literally only had a couple of feet where I could position my notebook to stay in the signal pattern. If I took a step sideways either way, it was out of the pattern and I couldn't get on the network.
If you don't know where the signal is coming from, this will certainly help you find it, but once you've done that you need to bridge that network into something else local for it to really work good.
