I had an informal sit-down interview with a couple of Apple reps at my school. We just went over a couple of things on my resume and talked a great deal about Apple. I think what really helped me stand out was showing my enthusiasm by asking a lot of technical questions about manufacturing (what I was interested in). They're not just looking for smart people, they want motivated people.
So that got me an on-site interview with the Operations/Manufacturing Design group about 4 weeks later. Honestly, I was surprised because it seemed like I didn't need to do much to get on-site. Oh well. I was flown to Cupertino for 3 days (Thurs-Sat). Interview was all day Friday. I had 6 30-min interviews scheduled, but really there were more interviews. HR adds in some extra "down time" where random managers can come to interview or re-interview you. Overall the interviews are not bad, some are more structured with HR questions, some walk you through technical questions (how would you measure this dimensions, how would you assure quality of this part). It shouldn't be too bad for a well-trained engineer. Just know, interviews are not done until you go home at around 8PM. So even when the schedule says interviews end at 3, they can come and interview you later, even during the "reception". So don't let your guard down.
Key things: Be enthusiastic and show your desire to work on Apple products. They want people who will buy in to their products. Bring examples of your work, if you can. Written portfolios or even a manufacturing project you worked on. I definitely used this to show my work and it paid off with an offer. The people at Apple are very visual, and will appreciate this.