Personas as lived vs. documented
Andrew Hinton has wise things to say about what personas are and aren't in this article on Boxes & Arrows.. He reminds us that personas should not merely be an item in our methodology checklist. If they don't have a real impact on how we make decisions, they're not worth doing.
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."