Exactly. Part of using the wireless setup is knowing how to secure it. If people insist on going to thier isp and saying yeah, just give me the hardware I will do it myself. They are asking for trouble.
I know of several friends who go roaming around in their cars just begging to find people who do not protect their wireless setup.
The results can be quite frustrating for the end user, who then calls someone like me and says what the heck ... and I say well how did you secure your wireless connection. Usually they respond with, well how do you secure it, I'm a complete idiot when it comes to these things. To which I reply, well why did you not get us to set it up for you in the first place?
But then again, if it weren't for these types of users, I would be fairly bored at work.
And to answer your question somewhat, yes you can do many things if you tap into a non-secured wireless network. One of which is connecting to peripherals on the network. Just be smart about it.
~Fawks