Yahoo Software Developer interview questions

I had two phone screens. The first phone screen consisted of coding questions (how to print a singly linked list backwards) and the second phone screen was a conversation with the hiring mgr in which we talked about past projects I have worked on. These phone screens occurred over the course of 2 weeks. Next I was invited on site to speak with 4 people. After 2 weeks I was told that I was not selected for the position.

1 phone screen interview, followed by 3 days of 5-people interviews (+lunch interview) in a period of 1-2 weeks. Interviewed with people from 3+ teams different from the one that phone-screened me. Finally the team that phone-screened me hired me. After I accepted the offer, while wrapping up my work in my previous company, the recruiter asked me to have a letter signed by my previous employer showing that I have completed everything we discussed when I gave them the 2-week notice, which I thought was unusual.