I submitted my resume cold through Amazon's careers site, and about one month later received an invitation to fly out to Seattle for an interview event. Amazon was very accommodating with the expense coverage and hotel (2 nights, the importance of which really can't be overstated), and made the trip my favorite interview trip that I've had, including trips to NYC and San Francisco.
As is common knowledge, Amazon is in a phase of rapid expansion, and as such is doing its best to scoop up the top talent in the field to help them grow with continued quality. Their interview format reflects these needs, and is quite unique among top-tier software companies. Roughly 20-25 candidates were flown out for this event, and we were all taken to a large room to be briefed. In the room were multiple small tables with 3 laptops and name placards each, and we separated into our designated groups (of 3, as mentioned above). Each group was then given a detailed problem statement, and we then proceeded to spend the rest of the day working with our team to develop a solution, coding our (self-chosen) parts individually, and talking with Amazon engineers about our understanding of the problem, our design, and our progress with our solution. It was not as academic (read: knowledge-based) of an interview as those at Google, and the problems were certainly non-trivial.
Although initially I was skeptical of this interview format, being used to the traditionally revered 4-interviews-with-a-whiteboard format used elsewhere, I found myself enjoying and respecting this interview format more and more as the day progressed, and ultimately, I found that I far preferred this to the traditional format. It allows the engineers to judge teamwork, leadership ability, personality, confidence, and communication skills, as well as providing a no-nonsense way to find out if a candidate can analyze a problem and ship effective, maintainable code in the span of a day in a quality-critical environment, which is really what is the ultimate goal of these interviews. As such, I'm a believer in this and other alternatives to the traditional interview format, and I applaud Amazon for doing what it can to find a better way to do things.