I applied through our on campus recruiting website and received an email a few days later inviting me to a phone interview. The phone interview was quick but pleasant. We talked a little bit about Microsoft and then dove right in to theoretical marketing questions. I think the recruiter was just trying to get a feel for how I thought about the questions.
About 3 days after the phone interview I was invited to fly out to Seattle for an intern interview day. They were very accommodating in providing hotel rooms, rental cars, and daily meal budgets. The interview day itself started with a group of about 20 candidates mingling with current employees and having some general questions answered in an informal setting. Then each candidate had 4 interviews with 4 different people from the company (different divisions, different levels of seniority). The interviews were very relaxed and low pressure. They then shuttled us back to the hotel for the night. I received an email extending me an offer before I got home from the trip.