Have had several interviews with Apple (for new grad/intern), here's what I've gathered.
Process
-HR doesn't communicate very well (or at all) with other HR reps. Apply for multiple positions (if applicable).
-You'll do an initial phone screen with the "Manager". Followed by 2-3 (3 is typical), with engineers within that team. From there, they'll do a full-day onsite grilling fest.
-Interviews are very scripted and directed. Probably due to the sheer amount of candidates, questions tend to be very generic and/or involve classical responses.
-It's typical for them to be late/tired or rushed. Honestly, this alone sends the wrong signals.
-Very little communication regarding applicant status. Be assertive. Rule of thumb is, if you fail to hear back within the next couple of days, it's not happening.
Materials
-It varies.
-Some interviews like to play the syntactic pop trivia question game (what's a static member, memory segments, etc). Be warned, sometimes the question doesn't have a "easy/clean" answer (i.e. impL specific).
-Situational answers (If you pissed off a co-worker...etc), not as frequent.
-Some behavioral (not typical).
-Most of it is problems. Study data structures, algorithms, and classical approaches to typical CS related situations (How do you think spell check is impL? Complexity of a phone queue? Real life deadlock?).
-Questions seem to be regurgitated and/or spun off classical questions.
Responses/Feedback
-You won't get ANY feedback.
-Asking about culture, motivations, is probably a waste of time.
-Be honest, concise, & elaborate if needed, and say. "I dont know" if you... don't know.
Overall
-I love Apple as a company. I love their products. But the HR dept seems be borderline laughable. I think it's the quantity over quality issue (in screening). Canned rejection responses are typical, and I wouldn't sweat not getting the gig. You can easily try in another area. I feel the HR department is nearly a reflection of the company within, and I'm by no means impressed.