The only example I have seen is plentyoffish.com. According to this: http://www.inc.com/magazine/20090101/and-the-money-comes-rol... the guy who owns this works barely an hour a day and earns more than 4M$ in revenue of it.
They're just slightly above 419 scammers.
I've been involved with a friend's site that pretty well fits the category. After some initial programming, SEO, etc, it did very well for 2+ years (> $100k revenue), but user support grew and grew, and then clones popped up, and started ranking ahead of him in Google results, then the revenue dropped to next to nothing. He could invest more time to get back to the revenue level he was at, but I just think that's the natural cycle for "passive" web sites.
Things go wrong, competition appears, users never quite fit the mold you want them to fit in, bad things happen externally...