It is amazing how many open wireless ‘networks’ there are in airports and hotels. Often times they have names like ‘linksys’ or ‘Free Public Wifi. They look familiar, friendly and harmless, but they might not be.
You see, most of these networks are actually peoples computers and not a wireless access point. Different wireless clients do a better or worse job identifying ad-hoc computer-to-computer networks. The problem is that if you connect to an ad-hoc ‘linksys’ network once, you may accidentally add it to your trusted networks. That means the next time you are in an airport or hotel and some jack-ass has set up a similar network, you will be connecting automatically.
When I stop to think about it, I think the prevalence of thse networks has more to do with ignorance than malice. I imagine there are a fair amount of novice computer users who try to configure a new wireless network on their computer and accidentally make themselves an open network. Of course, that is a danger that would have it’s own set of problems.
I would feel much safer if I was traveling with a Mac. 
