I found a link to this site www.usbwifi.orcon.net.nz . They are using
inexpensive kitchen items to make cheap parabolic dishes to use with usb
wifi dongles.  They claim some of the antennas get 15-18 db gain.

Joseph Key 

Twin Cities Wireless Users Group Mailing List - Minneapolis/St. Paul, Minnesota
tcwug-list at tcwug.org