The process took 1 day. I interviewed at 3M in May 2011
Interview
It was well organized. First, a HR will give you breif introduction of their company and products. And then introduce their managers from various branch worldwide. After that, you will be asked to take an 1 on 1 interview. I think this is just the first interview of the three. They mainly asked about your situation, degree, and the projects you have done before.