Archetypes not Personas
I firmly believe that while embarking on discovery research for a User Experience that archetypes are a better, more accurate model than personas.
When your UX team creates personas — they are creating fictional characters that represent your user base. Personas include details such as age, sex, occupation, education, interests and more. These personas are often created in a vacuum — with little insight into their behavior. A UX team will assume a Female, 18-25 years old, with a high education level will experience a product one particular way. This often leads to bending the persona to wrongly validate a design decision. A person's characteristics and behavior do not always align. The difference between characteristics and behavior, in some cases, could be very volatile.
Archetypes are modeled around a behavioral perspective. Examples of an archetypes could be a leisure browser, photography centric, task centric, or identity centric models. Using archetypes gives us a better view of behavior in interaction design.
For example: A photography centric user may scroll through their social network newsfeed with the primary goal of consuming media in the form on photos. If this archetype model is a high use case for this social network — they should adopt a photo stream (think Facebook Camera). With the knowledge of a high use case for an archetype, they can model their interaction design around the goals of those specific users. This could include image modals to view full resolution photos, seamless keyboard navigation, and filter/sorting capabilities.
Archetypes are a great model to validate interactive elements and user flows at a macro level. As you add more features to your interface it's encouraged to revisit these archetypes. When new features are added or removed the behavior of a user will often change as well. Archetypes + data is a more accurate UX strategy than creating personas.
Let me hear your thoughts, opinions - Follow me @PaulFarino
EDIT (11/5/2013) :: Input from Kyle Bollinger (modified)
“…Personas are essentially a design tool to create empathy with a group of real users./ …The purpose of personas is to mix demographic information with archetypal behaviors in a believable and true to data harmony.”
Suggested Reads: IDF’s chapter on personas | About Face 3