I got a Cantenna as a Christmas present for She Who Is Perfect In All Ways. Before I get angry comments, I should note that this was specifically mentioned as a possible present. SWIPIAW was interested in trying it out for war-driving as part of her network security teaching / research. However, what she discovered is that such things are harder than they used to be because of technological advances. In particular, laptop network cards no longer have external attennas. These are now built in to the cards. That makes upgrading the attenna for greater range (definitely a feature for the war driver) somewhat more difficult.
Not a big thing, but somewhat amusing. It does look there are still a few 802.11 cards with external antenna jacks, but they’re no longer something you can pick up at your standard computer retail store.