I like the idea of a scale or some kind of label to let people know what level of research went into each persona. Of course, I see a core distinction between qualitative personas and quantitative personas. Perhaps one metric behind any persona should be the number of actual users that shaped this persona (in interviews, field studies, surveys, etc.).

I love this bit: "Personas are not documents, and they are not the result of a step-by-step method that automagically pops out convenient facsimiles of your users. Personas are actually the designer’s focused act of empathetic imagination, grounded in first-hand user knowledge."

The challenge is that the quantitative data could be placed on top of incorrect qualitative personas right from the start. If the personas you invent aren't right, no amount of data on top will help. That's why I'm a fan of the quantitative persona creation process, where data from surveys and Web analytics gets used via statistical analysis to generate the persona segmentation in the first place.

Make sure to read the good discussion after her article.

Sometimes a team gets lucky because they truly are their audience. 37signals creates products that are amazing because they are designing for themselves and many people are just like them. They don't need personas. But most of us don't have that luxury. We don't live and breathe what our users live and breathe, so we need tools to help us gain empathy, understand stated and unstated user needs, and translate that knowledge into action. Personas aren't a panacea, but they can go a long way to helping team members have a shared vision for what the site or product needs to do and how.