It was highly effective. Catapulted a few local businesses (I believe one gained enough exposure to open a second location) and a few temporary internet celebrities owed at least some of their fame to it.

That said, the latter example on YouTube was not effective at all, but that was probably because the content wasn't great.

not op, but this is essentially what SEO boils down to. More links to your site from legitimate sites with high page rank push your site up the natural listings.

It doesn't matter how 'pure' a site is, you can still buy a link, it just costs more.

It's all about looking at how the algorithm works, then gaming it. Tinker with Twitter and facebook, spend some money, keep the results secret. Sell this information. Do what works to your clients.

Bot nets work. For now. Does Twitter want to kill them? Maybe not, active accounts is a big number that they love to tell people.