To start with the HR at Yahoo are very helpful. They help solve all the doubts you have. On the day of my interview I along with 10-12 other candidates were taken into a room where there was lunch and a small presentation on what company does. It was followed by 4 rounds of technical interview. The topics ranging from Data Structures and Algos to design question and Optimization questions. The interviewers were quite friendly. Overall a great experience.