From a 100mW 3dB omni-directional antenna fitted to an Aironet access point in a metal comms cage in a metal aircraft hanger at Blackpool airport, I got a range of over 1 mile using a laptop PCMCIA card with 2" antenna.

Using Symbol kit with directional 6dB Huber Suhner patch antennas I have got successful connectivity at 5.5 Mb/s at over 6 miles.

I have had longer distances with wierd antennas, but they probably don't meet licencing regs.
Those are pretty impresive ranges. How did you secure it, since you also presumably have greater range for hackers...

-jk