This week-end I finally bought a wireless router and a PCMCIA wireless card for my laptop (802.11 network). Prices are so low now, you can have that for almost the same price as two stops to the gas station ($2.15 a gallon here in California, yuks)! The router is connected to the DSL modem (or cable), and you don't even need an ethernet cable to surf the web. Finally I can surf the internet from my bathroom. A big improvement in the quality of life!:-)
Saturday I got everything working, it does not seem to care much about walls, perfect reception in every room of my apartment. It is also pretty easy to configure, the default settings work just fine.
The next day, I turn my computer on in the morning to check my emails, and after a few minutes of websurfing, I realize my router was turned off?!?!?! It still works!

I check the status of my wireless card and realized it found another wireless access point and connected to it without any problem. I am assuming my neighbor has a compatible equipment;-)
So basically this is what happens if you let your router run with the default settings, everybody close enough could potentially connect to it and surf the web. Someone could download mp3s all night long, go to child pornographic web sites and you will be the one liable, it is your IP address. To the least it may be a real pain to prove it was not you. So my advice if you switch to wireless don't be lazy, change those defaults and add some security! You are never too paranoid so I just changed mine to the maximum security available on my router, MAC filtering, 128-bit encryption, etc...

Good tips to protect your wireless network:
http://www.arstechnica.com/paedia/w/wireless-security-howto/home-802.11b-1.html