Just like any development or UX tool, personas can be dangerous or super effective. It has nothing to do with the concept of personas, it's just how people choose to research and use them. The intent isn't to design for a specific customer, it's to give the UX and development teams a common user reference point to validate their assumptions against through user interviews and continued research, iterating on the personas.

I'm sure you know about Alan Cooper's books, but another that I've found helps maximize the benefit, and minimize the danger, of personas is Tamara Adlin's "The Persona Lifecycle" : http://www.amazon.com/Persona-Lifecycle-Throughout-Interacti...

Plus, Microsoft isn't exactly known for it's effective UX.