Broadband for free

I've finally moved out of my squat, into my new house. It's very nice. But that's not really interesting. What is interesting is Rory my new house mate wanted to check his Email. We don't even have a phone line yet. "No problem" says he and proceeds to hit a few keys and a box came up "scanning".
"Here we go, I've got a live one."
"Got what?"
"Someone near here with a wireless connection."
"And?"
"I'll piggy back their wireless connection and get my email."
"You can do that?"
"Of course."
"Will they know."
"No but their computer might start running a bit slow."
So Rory checked his Emails and I got to thinking. Is this a bit of fun or is it something darker? Is it ethical to piggy back someone elses wireless connection?
I know it's nothing new. I've read of people driving around looking for a wireless signal to get connected when they are away from home. But I've never seen it done.
So while it was a lot of fun. It did leave me wondering if it was right. But then for someone who just spent the last six and a half years living scot free in a squat I can't talk.

Rock on dudes