In two recent posts by Nishant Kaushik of Oracle (Part 1 & Part 2), he has made some very good observations around understanding the process of defining roles as part of an Identity Management infrastructure.
As can be clearly seen from his posts and my experience (and probably lots of others out there), there is no single process that will be right or suitable for all organizations. As usual, it all depends on the individual circumstances of the organization and what they are trying to achieve.
Great post Nishant!