Business casual, smart pants and a nice shirt tucked in. Blazer optional. Absolutely no tie or suit. Play on the safe side with the shoes.
Excellent advice and I agree with it.
The point about interviews - even interviews that stress how 'casual' the whole thing is supposed to be - is that you are being judged as to whether or not the interviewers think you are suitable for the position in question. So, while how much you like, know about, and love Apple is only a part (a large part, granted) of the interview, other factors also, often come into play as well. Such judgements - like it or not - are often subconscious - and based on a myriad of subjective factors, such as appearance, attitude, demeanour and perceived personality.
So, despite appearances, a job interview is not a cup of coffee with a bunch of friends, - and I've had interviews where good filtered coffee and a really affable, pleasant ambience marked the process.
That means you must look as though you are taking the whole thing seriously, and with respect, which, in turn, means that you should look as though you take yourself - and what you have to offer - seriously, as well.
So, as niuniu said, smart pants - that means no jeans unless they are really new, well-cut, spotlessly clean, and fit you well. Chinos/khakis will probably do the trick. Again, a good shirt - that means a shirt with a collar, clean, and pressed (i.e. ironed), and yes, tucked in. Proper shoes, not runners, smart loafers will do if you have them.
Good luck
