The Pringles Cantenna gets a bad rap: A few days ago, a hapless police lieutenant gets quoted saying that cantennas are illegal. He told BoingBoing that he wasn't exactly misquoted but he understands that antennas in and of themselves are not illegal. (Although, technically, many but not all are against FCC Part 15 rules.)
The (Cleveland, Ohio) Plain Dealer has a funny and accurate article about stealing Internet access from others which quotes a local IT security firm's head as saying, "A Pringles can and antenna can extend a Wi-Fi signal...It's ridiculous."
But the fellow isn't saying that Cantennas are bad, but rather that it's absurd how easy it is to tap into networks. The article suggests that security is just 15 steps away.