The process took 2 days. I interviewed at IBM (Washington, DC) in Oct 2011
Interview
First round phone interview. If selected to interview in person, flown to interview location (expenses paid). 3 back-to-back 1:1 interviews, including 1 simple case interview. Process was well-organized, people were nice and helpful, though some interviewers weren't very enthusiastic about their work when asked. Turnaround time to an offer was fairly quick.
I applied through college or university. The process took 2 weeks. I interviewed at IBM (Washington, DC) in Sep 2011
Interview
I applied for the position through my schools career center website. I also had an alumnus from my program refer me.
The interview was 3, 30 minute interviews. 2 if the interview were behavioral, asking me about my experiences, and going over my resume. They also asked me multiple times why I wanted to work in consulting and for IBM specifically. Additionally, they asked about how I work in groups multiple times.
The 3rd interview was a case interview. This was the first year they have used cases. I was asked how I would help a health care company who had problems with their patient tracking software. I was told to explain how I would asses their problem, walk through a solution, and how I would implement the solution. I didn't use any case interview framework, and it was pretty informal. I did take notes though, and made sure to be logical, methodical, and summarize at the end.
About 2 weeks later I received a phone call offering me a position. While I was waiting for a formal written offer, I was asked to come into one of their offices. I had what amounted to another interview, where someone went through my resume and experiences. A few days later I received another phone call offering me a higher salary and sign on bonus.
My advice: When giving examples, be sure to answer the question asked, and follow the formula of explaining the situation, explaining what you did, and explaining the impact of your actions. Also, be prepared to tell them why you want to work for them.