I'm going to be looking for an internship somewhere next year, maybe I should be going in the US !
My understanding is that one receives 1.5 times their typical salary after eight hours and twice their typical pay after 12 hours. Some students are willing to put in the occasional 100 hour week when internships only last four months. Considering the base salary Apple offers is already relatively substantial (speaking as a student, at least) that can be quite a lot of money.
