If you live in a populated area you can pick up signals from other wireless connections.
If they are not password protected you can piggy back on.
What IP address is used?
yours?
Is that a safe way to hide your identity?

your mac address may be recorded by the source of the signal.

Not a good idea.

Dear Lovers Rock:
The underlying question is can you spoof your ip address. If you can spoof or mask your ip address that is half the battle. However if can also be cross referenced by your hard coded address. That is the concomitant of your dna. Henceforth you can fake the funk on that one. However if you can find the algorithm to login on a closed network then you can get in. However you might be in a place where they are not that technologically prudent so you could get away with that considering that you are near the access points were you are picking up a signal.