In our new book, Entrepreneur's Guide to The Lean Brand, Jeremiah Gardner and I tackle how relationships build passionate customers. In our view, products should fulfill a utility promise -- this functionality solves a that specific problem. But fulfilling the promise can only create 'satisfaction.' (Not always true, but generally.) It's the relationships between company and employees with customers that potentially creates 'passion,' which is required for scalable growth. So how do you measure passion? Probably not in one particular way. Some combination of things like Net Promoter Score, Must-Have Score; social-media campaigns that measure participatory behavior; increase sharing of content; increase in viral-coefficient (OK for non-network effect business < 1!). Early on, the best way to establish relationships is by meeting customers in person, in order to understand them deeply and develop empathy. Hypothesize 'what behavior can I expect from a customer with whom I've developed a relationship?' Measure whether that behavior is occurring.

Ries owns 'Lean Startup' trademark. I doubt 'lean' by itself is trademark-able, and isn't claimed by Eric. Someone else may claim 'lean career development,' so might be worth a trademark search.

In The Lean Entrepreneur I discuss how to create a segment matrix: put your different segments in rows (hopefully these are NARROWLY defined!); in columns, come up with salient criteria to measure segment worthiness. It's ultimately up to you, but might include "Depth of Need", Budget, "Ease of Reach" (marketing), etc. Could even include things like "Matches Values." Be sure to write in such a way that a High-Medium-Low ranking is consistent across criteria. In other words a High Depth of Need is a good thing, so other high scores must be a "good" indicator. Rank each segment in the criteria High, Medium, or Low. It's OK to guess at this point, but your customer discovery should attempt to validate the values. It's likely that 1 or 2 segments will rise to the top.

Christopher provides an excellent answer. The one thing I might add is: be wary of dev shop claims to understand what an MVP is. Despite the success of Lean Startup, I'd argue most dev shops still don't know how to build and iterate MVPs. It sort of runs counter to their business model.