Judging from interviews, when Zuckerberg starts explaining something complicated, he stops trying to charm the interviewer and just focuses on the middle distance and lets his face go blank. His expression isn't hostile like in Eisenberg's performance, it's just neutral because he's concentrating on the logic of what he's trying to say. He's a monotasker. (I do the same thing -- if I'm being engaging and personable, well, you can tell I'm not thinking that hard. But, if I stop looking at you and start speaking in a monotone, then I probably found your question very interesting.) When Zuckerberg tries to spin something he did for money, like the recent privacy default settings imbroglio, he tends to sweat a lot: in other words, he's not an expert conman. This awkwardness makes it easy for The Social Network to attack Zuckerberg, but I like that in somebody that rich and powerful.
For example, unlike all the millions who go on Facebook (or Twitter or their blog) to alert their hundreds of close friends that they are going to the grocery store to pick up a gallon of milk and some toilet paper, Zuckerberg is quite private. And, relative to most billionaires (and contrary to the impression fostered by the movie), he also doesn't seem to be that socially or sexually ambitious, as the paparazzi pictures from Roissy's blog that I linked to in my review of the movie suggest.
Zuckerberg is a fish who notices that he, and all the other fish, are wet.
If my one important insight is that race and genealogy are more or less all part of the same thing -- that a racial group is a partly inbred extended family, a definition that makes how the world works simpler to understand in many ways -- then the reason I noticed that in the abstract is because I care a little bit less than most people about things like race and genealogy at the personal level. For a variety of reasons, I'm slightly less invested emotionally in such things than the median person.