November 8, 2007
I realize I'm not going for any world records with a 100 km WiFi link. Many have gone before me; here is a partial list.
In July, 2005, a group set a then-world-record with a 201 km link. They achieved 11 Mb/s (perhaps link speed) over this distance using huge home-made dishes (3.0 and 3.7 meters) and 300 mW Z-Com PCMCIA radios. More details can be found here, here, and here.
Also in 2005, another group successfully connected a 420 km link between a ground station and a stratospheric balloon. According to Pietrosemoli, they used 6 watt amplifiers to boost the signal strength.
In April, 2006, Ermanno Pietrosemoli and his team used Linksys hardware on a 279 km link (this version has additional photos). They used a signal generator and spectrum analyzer for aiming only, and adjusted the ACK timing using OpenWrt. Based on a screen shot of their file transfers, it looks like they were getting around 70 Kb/s throughput.
In February, 2007, Ermanno et al tested a 101 km link. Here are some pictures of the test. They used 28 dBi solid dish antennas, Soekris boards (and one Metrix board), and software developed by the Berkeley TIER group.
In April, 2007, Ermanno et al achieved another 279 km link, but this time with about 3 Mb/s throughput in each direction. They used commercial HyperLink 30 dBi antennas and software from the TIER group again.
Also in April, 2007, the same team set up a 382 km link using the same hardware. As far as I know, this is the current record without using amplifiers. However, in Ermanno's words, "This link proved to lack stability, and we would loose connection from time to time." More details can be found here and here.
Wikipedia has a short article on this topic.