I had an on-site interview, which is much better than phone interviews. Usually they just check out what your background is and see what practical design knowledge you have. I haven't had the math quiz that other companies have had, maybe those were just phone screens.
The people/managers vary wildly between organizations. Some are much more helpful during the interview while others seem more skeptical. One interview gave me the impression that the work/life balance wouldn' be there. The culture seems to be very negative right now.