That's a good question. LinkedIn ranking high makes sense but we were really surprised by about.me. Here's a high-level answer

1) LinkedIn tends to rank high because, not only is it a well structured page, but people tend to take the time and fill out all the information. From Google's perspective, the more relevant information about someone on a page, the higher it should rank. Think about it: Twitter gives you 160 characters, and most people barely fill out their FB profiles beyond status updates. On LinkedIn however, people carefully fill out their bio, their headline, all of their education and work experience. They post their resume, get reccomendations, plaster their name everywhere, etc.

2) Why does about.me rank so poorly? On the other end, about.me is structured pretty poorly. You aren't encouraged to publish much content and the page remains relatively static and sparse. Compare that to twitter. Sure on twitter you only get 160 characters in your bio, but it's constantly updating with new content, which Google loves. About.me basically has the worst of both worlds: Not much original content, streams duplicate content from other places, which Google doesn't favor