I did three rounds before I had to let them know I accepted another offer. I feel they would have made an offer had I not secured another job.
First round - technical screen
Second round - business/consulting screen with Business Development Manager
Third round - screen by CTO (the hardest of the three)
All the interviewers were intelligent and asked good questions.
From the initial application to the time I let them know I had found another job was ~45 days. I do feel if the process had gone a little faster I would have gotten an offer and possibly working there today.