I think a good rule of thumb at this point is to be extremely skeptical of anything advertising supported. If people won't pay you, are you really creating enough value to society to justify awarding yourself any warm fuzzies?

I suppose exceptions could be made for services like Google, which people would pay $1000/year for if that's what all the providers charged, but which happen to be advertising-supported.

"Make something people want enough to pay for." Now there's a terrifying heuristic.