I hope he's diversified enough and not too reliant about Adsense. Its great when it goes well but every now and again a bad month hits and its good to have a back up.

Its a great lifestyle though - working at home, flexible hours (lots of them but flexible), good money and interesting work. I love it.

It's a perfectly valid goal to which to be able to live off of your AdSense earnings alone, whether or not you actually choose to "quit your day job" (or, for the already self-employed, sever your other income streams).

Anybody who has been self-employed for long enough, or has been around other self-employed individuals (or even small businesses) for long enough, probably has a horror story about somebody who had to rebuild after losing the client who was responsible for half or more of their revenue.