This is Andrei. You'd be surprised; the interview was very difficult and I might have failed it just as easily. I got no C++ question (we seldom ask language-specific questions). Instead, my interviewers asked me questions related to my research and had me implement a classic algorithm on a very large data set and a simple ML algorithm. I recall at a point I got the curve ball of an NP-complete algorithm that had a polynomial approximation.
Bottom line, the Facebook interview is not easy, and we're determined to not make it easier even though we're hiring intensively. The upside is that you get to work almost exclusively with very bright people, which makes for a very palpable difference from the typical corporate experience.