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.
Is it just me, or does that seem terribly scummy. I'm not sure I'd consider inserting additional ads to be an ethical problem, as long as it was clear which ads came from the browser plugin, and which ones came from the website. But IMHO replacing the website's ads is scummy.