Very thorough - three separate onsite interviews with multiple people. Initial phone call with recruiter was half an hour long, just a quick resume review and typical "what do you want out of a job" questions. Technical people asked high level technical questions, even though it is not really a technical job, to make sure you understand the technology you will support. Lots of troubleshooting questions, hypothetical situations, etc.
Know your resume! They will read it (all of it) and quiz you about it. Even stuff from a decade ago. Be honest and be enthusiastic about the company and the position.
Everyone I interviewed with was enthusiastic about working for Apple and seemed to enjoy their jobs.