I believe nearly all of their data is just pulled from the big 3 search engines, especially Google. They also grab page ranks, backlinks from yahoo, adwords dat

I believe nearly all of their data is just pulled from the big 3 search engines, especially Google. They also grab page ranks, backlinks from yahoo, adwords data, and microsoft oci data. It's not proprietary data, it's just presented really well and saves a hell of a lot of time