I just happened to check and saw that my HP Adsense is at $103.71 today.
I don't have to wait for a payout as that money is combined with my other sites earnings and is always more than needed, but if this were my only source, I would have just reached it.
It took 8 months. I do little outside promotion except Facebook and Twitter, and do not use keyword research (not that I don't think you should; I'm simply too lazy).
Of course I do have a lot of hubs. Most of them get very little traffic at this point and some (about 10%) have had nothing in the past 30 days. Total overall traffic since I started is still under 40,000 views.
My point is just that I do everything "wrong" and still make a little money. I make the same errors at my main site, though that's both much older and larger, so I make much more.
It is possible to just write and make money. The monthly HP earnings have been steadily increasing, though they are a little flat for January.
Now imagine what someone could do if they wrote well researched hubs on good keyword choices and promoted them well..