Can someone make a long-term career at online poker?

Some of the replies in this post and many of the those in other posts show why online poker is profitable.

You don't have to be great, or even a particularly good player to make money (just better than enough of those players who know obsolutley nothing, to out-perform the rake). I started 3 months ago, keep records and don't play full-time. I have put zero cents (zilch, nothing) into poker accounts; started out from free-rolls and no-deposit cash bonuses. I have taken out over $300 (not a fortune, but from 0.5 / 1 no-limit games it's not a lucky streak either).