A trend is reversing it seems... In 2005 the majority of the households that had installed wireless access points did not lock them. Five years later however I notice that 100% of the networks in the neighborhoods I visit are locked.
I share my home Internet connection with my neighbors and I encourage you to do so too by unlocking your access point. If you are in the Berkley,MI area and notice an access point named "free_net_berkley" - feel free to use the traffic however you want. I am indeed working on convincing my neighbors to unlock their wireless routers as well.
Why?
First because it is hospitable. Why not help people connect to the network once in a while...
Second because it weakens government and big corporations' surveillance power.
An excerpt from Richard Stallman's "Digital Inclusion in Freedom"
"We can take direct action to protect others' freedom in the digital world. For instance, we can remove the passwords from our wireless networks—it is safe, and it weakens government surveillance power. (The way to protect the privacy of our own Internet communications, to the extent that it is possible, is with end-to-end encryption.) If others use enough of the bandwidth to cause actual inconvenience, we need to protect ourselves, but we can try gentle methods first (such as talking with the neighbors, or setting a password occasionally for a day or two), and keep the option of a permanent password as a last resort." full article
Another great discussion on why you should run an open wireless network at home