There were no questions that stood out as truly difficult. It didn't appear they were trying to stump you, but rather get to know you. On the other hand, many of the questions had multiple parts (which are read at once), so don't be afraid to ask them to repeat a part of the question. I did it multiple times. My best advice would be to think of several projects you have worked on in the past and know them in and out. Be prepared to answer questions about issues you had during design (time, flaws, restrictions, process), but nothing really technical. Also think of the interactions you had with team members and how you handled the more difficult situations. Come to think of it, one difficult question was: Describe a time that I disagreed with a superior and explain how I handled it.
