The service is centered around Fonera, a WiFi router that just got upgraded to version 2.0, and although most users aren't that interested in hardware that powers their Wi-Fi network, the new Fonera has so much to offer that it alone is reason enough to try out the service.
First of all, every Fonera creates two Wi-Fi networks: one private, for your use only, and other public, for other Foneros to use; of course, every user can set how much bandwidth and resources he/she is willing to share. Fonera also doubles as a simple NAS (Network Attached Storage), and has a USB connection, which means you can connect a USB hard drive to it and download torrents, or upload stuff to Facebook, Flickr or YouTube even with your computer turned off. It lets you automatically backup your data, and finally, it supports 802.11n, which makes it faster than the old version which supported the older standard, 802.11g.
Now, while features such as these were quite irrelevant a couple of years ago, today, when every household has a couple of computers and laptops, a centralized Wi-Fi router which doubles as a NAS is a great idea. Of course, as any system admin knows, not all NASes are created equal; it'll be interesting to see how well Fonera 2.0 performs in terms of data transfer speed and reliability in real life situations.
Depending on the country you're living in, the price for Fonera is different; in the US, it's $39.95, while in Europe it's €49,95. Furthermore, FON might not be legal everywhere; in some countries, it's illegal to share or resell your internet connection to third parties, and in some countries FON is simply not available.