Cantenna – do these things work?

There’s this device called the Cantenna that you can buy, that connects to your laptop and is supposed to greatly extend its wireless range, allowing you to find more wireless networks to jump on to.

Here’s what I’m thinking: There’s free wireless Internet at Court Square. I live at 10 South Main, about a block away. I wonder, if I bought a Cantenna and pointed it at Court Square, would I get a steady, fast, reliable connection? Because if I could, and I knew I could depend on it whenever I’m at home, then I could get rid of Road Runner and save myself 45 bucks a month.

Has anyone tried one of these Cantennas? Do they work? By how much do they extend your range? If you have experience with these, could you please shoot me an e-mail and let me know what you think. Thanks.