The best interview experience in my career, and I've been to quite a few interviews.
After an email, I got a call for a phone screening. For some reason I was expecting HR person, instead talked to the hiring manager. He asked just the right questions that painted an exact picture of my skill level - how much I do know and where are the limits of my knowledge and experience. In general, I'm straightforward and honest person when it comes to interviews, I don't exaggerate my skills to present in a better light. But still it was uncanny how the person asked the questions that will give an accurate idea of me as a developer and employee. Usually you can cheat your way through an interview process, but not with Yahoo.
Then there was an onsite interview with 4 people and the hiring manager again before and after the others, including informal chat over coffee in the excellent Santa Monica Yahoo! Center.
Overall very challenging phone screening and a relaxed and friendly onsite experience.