Computerworld reports that in testing at airports, they found honeypots intended to lure unsuspecting users: I'm a bit lagging on this story, reported two weeks ago, but it's still relevant. The "Free Wi-Fi" scam involves password snatchers setting up fake Wi-Fi networks in public places, like airports, that use free in their network name. Connecting to these locations puts your machine at risk. Further, for Windows users, your laptop might connect in the future to other identically named locations without asking if you want to connect. The attacker can snarf unprotected passwords and unencrypted email, as well as infect your computer.
Computerworld cites security firm Authentium as having found dozens of "free," ad-hoc wireless networks of this sort at airports across the U.S. The firm told Computerworld that in multiple visits to O'Hare, they found over 20 ad-hoc networks advertising free service each time, and saw "fake or misleading" MAC addresses, the numbers designed to identify each Wi-Fi or Ethernet adapter uniquely.
The article offers specific advice on how to avoid this problem. The most prominent in my mind? Use a VPN. Several firms offer VPN-for-hire for travelers who don't work for companies that offer or require VPN use on the road. Try JiWire's Hotspot Helper (Windows only, $25/year) or WiTopia.net's personalVPN (Windows/Mac, $40/year), for instance.
(Disclosure: I have a very small stake in JiWire.)