The guys at 37signals have explained why they don’t like or use personas when developing new applications. Make sure to read the interesting discussion in the comments.

I couldn’t agree more. They use personas to a great extend at work, and I fail to see the use of them. It’s said that personas put a personal human face on otherwise abstract data about customers and while that’s good the problem is that I as a developer have no relationship with this guy with the personal human face. It’s not an actual person I can put a prototype in front of. It’s not someone I can ask a question. When I ask the persona something it’s me pretending to be something I’m not answering, and that can never be good.

In my option real users is the key.