Part of our user-centered web design process includes the development of personas through research and analysis. Personas have a noticeable advantage over traditional demographics because we (you, me, clients, etc) can relate to a person far more naturally than a list of stats and demographics. It's human nature to bucket information into a way that you can remember, that you can relate to, that you can engage with - and a persona literally puts a name with a face on a fictional character that we can all discuss and create an amazing experience around.
So my big question is how far to go with the persona? How much detail is necessary to tell the story and paint the picture?