Unencrypted networks are a HUGE problem. You could go into an apartment or condo building and get five or so networks within range. Chances are you'll be able to connect to three or four of them without ANY key whatsever. I once accidently connected to my neighbors network (and I didn't notice at the time). I noticed that day when I went into the network folder and realized that the computer on the network were not the computers in my house. I went into one of them, and the entire C:/ root directory was shared (also a very bad idea, whether encrypted or not). At that point I went and set up WEP for them.
The lesson: Use WEP!
And no, this isn't unique to the Powerbook. Though using OS X, it would be generally be better in wireless networking...because NetZero (the XP wireless network configuration utility) in XP is something that needs to be worked on by Microsoft (disconnects randomly too much). Windows is seriously behind Linux and Mac OS X in the WiFi user experience as of now...hopefully there will be improvement in SP2...