Last Sunday's New York Times has an article that contains a detailed analysis of the soul-searching that Palantir is undergoing as it expands. The article has interviews with the founder of Palantir and its recruiter. It also has photos of the office.
http://www.nytimes.com/2014/06/01/business/unlocking-secrets...
The article mentions a cap of $450,000 a year in compensation ($137,000 salary + bonus $15,000 + $300,000 stock).
My 2 cents worth of advice would be to take the job and see how it works out for a year. After that, you are free to decide to go or stay, but with much better information at hand to make your decision.