I know some people there. They set a high technical bar, on par with Google (their reputation in SV is actually that they're tougher than Google/Facebook, which may or may not be true, I can't be too sure since the small sample of interview questions I've heard of were not any more difficult than Google questions). Expect a typical mix of algorithmic/systems design questions. Like Google/Facebook/etc, they draw heavily from elite colleges. Lots of Stanford, Harvard, MIT grads. The organization is very flat; not a lot of hierarchy.

The company itself is essentially an elite technology consulting firm (albeit one that is actually technically competent). They have a set of core generic products (they have a finance analysis product, government analysis product, some other ones). BWStearn's description is accurate (a tool for analyzing entities and their relationships). But the key to their success is they take that generic product and then dispatch teams of engineers to customize each deployment for each client (hence consulting). Often clients will hire them because the client has engineering talent and has to hire Palantir because of that.

From what I've noticed the culture does learn fratty, but I didn't find it uncomfortably fratty. However, the people there work hard and they work long hours.