The actual process was very odd -- I had submitted an online application for a generic job title at some point, forgotten about it, and then several months later received an unexpected email soliciting an interview. After a simple phone screening asking me to recap my resume, I was invited to an "interview event" (I don't remember exactly what they called it), that consisted of a short presentation by an HR consultant followed by a couple of interviews with Booz Allen staff lasting about 30 minutes apiece.
The first of these was a dull, cut-and-dried question-and-answer session asking for yet another resume recap, strengths, weaknesses, why this job, why this company, and so forth. The second was a "case" interview, though nothing like what I had heard case interviews for consulting firms were supposedly like. I was asked a very general question posing a client engagement scenario, and how I would approach the scoping and work if it were my project to run. There were no mind teasers, no mathematical questions, nothing even highly specific about the hypothetical engagement; it was mostly just an exercise in delineating a strategy for approaching a project.
After these interviews, I was presented with an offer over the phone within a week or two, and a formal letter following not long after that. Frankly one of the easiest interview processes I've gone though, and definitely not matching expectations in terms of rigor or level of difficulty that I expected from a firm in the management consulting industry.