Hah. I had an idea for a startup a while back that would provide free wifi to local businesses; the plan was to monetize by replacing ads with our own ads of similar sizes; I mean, the user doesn't care about the ads, right? so we'd get our money without annoying the user more.

I talked to a lawyer about it and was told that I'd get sued, and that I'd loose.

It is an interesting business model, if the lawyer was wrong.