Not uncommon Zoey, especially in apartments. People are lazy when it comes to privatizing wireless access points in the home with encryption and SSID broadcasting options.
My friend Mike was telling me last week that his son hijacks onto the web with his PSP through the neighbors wireless access point two houses away.
Also...
Becoming more common daily now, is that malls, book stores, and some businesses are offering wireless hotspots for clients as a convienence.