ok, here is a good example of how this could become an issue, it's only a matter of time before this actually happens.
A child molestor realizes that many families have insecure networks, and some of them even have wireless cameras, so he gets his laptop, installs some free software, and now he can drive around until he finds a family which has kids and a wireless network. With a few clicks of the mouse, he can now access the network, and find out what computers the kids use.
Since it's almost a given that the machines won't be up to date, he can now install real spyware on their machines, and monitor their activity. He could also start messaging the kids using the Windows Messenger service (or through a screen capture, he can find out what user names they have on AOL, MSN, etc.), and find them online.
I am sure I don't have to continue since most of you should be able to figure out what could happen next. Is this far fetched? Maybe, but it only takes 1 crazy person, and there are thousands of predators out there, just watch the news for a few minutes. I sincerely hope that if you are a parent, and you insist on having a wireless network, that you go with the latest technology which supports WPA/WPA2, and have it locked down as much as possible. Most people don't care if their data gets stolen, but there is much more at stake than just a few emails.