The question of whether or not AdSense is a secure way to make a living comes up every now and then. A new WebmasterWorld thread named Is AdSense a valid business model for publishers? goes right into that, and its three pages long already.
I know of a few people who have decided that their blog was bringing in enough monthly income. So they decided to move to a low cost area and continue their blog. I do not know if AdSense alone sustains their livelihood, but I do know they also have normal banner ads on their site.
The forum folks tend to believe AdSense is a viable and even sustainable source of income. But like any business model, there is always some risk.
Forum discussion at WebmasterWorld.