I've always had a twofold feeling towards user stories. Despite being critical about many drawbacks of the Use Case approach (the one I hate most is the time wasted in filling a template with the same useless information repeated over and over), I think that User Stories have some limitations that a team willing to turn agile has to be aware of.
Seven years ago, a younger me collecting requirements for a small application that should have handled the operations required to set up a secure banking account. Every person interviewed was telling me a different story in terms of "special cases" (the whole story seemed a collection of if … ), and the resulting workflow seemed messy and impossible to tame. I tried a different approach and started modeling considering states instead of actions. It turned out that the workflow was pretty simple, after realizing that there was no before-after correlation between some actions, and a loose workflow could have mastered the whole stuff with 2 screens, and a bunch of checkboxes.
JAOO Conference 2006. Jeff Sutherland talking about Scrum to a subjugated audience. Telling something like "If the product backlog is not ready, I give the whole development team a day off.". Silence. People dazed and confused. "There is no chance that any line of code written without knowing its purpose will turn useful. Instead we'll have to pay for writing that line, for testing that line, for refactoring that line and to convince the team that this line shouldn't be used.". Pause. "The other reason is that there is no better way to have the management hurry up and finalize their decisions than having the whole development team having a day off". I liked that.
Business application. Very complex domain. Requirements were heavily related to the Italian fiscal system (which means that the application should mimic the laws, but the laws are not intended to be understood, moreover many of them are flawed from a logical approach – but this is a whole different story, that can't fit here…). It took the lead analyst a couple of weeks to be able to nail down a specification for one of the complex use cases, and he was working together with the domain expert every day of the week.
Back to our story
One of the key points of user stories is that they act like placeholders of the real specification. Instead of writing a detailed spec, structured like a Use Case document, some months in advance, a User Story provides the minimum amount of information required to identify the story, estimate it, prioritize and relate it to other stories. Before development of that specific story starts, Story Cards serve basically as a low-fi management tool (estimation and prioritizing), allowing to defer the detailed requirement specification to the very last moment. This way, requirements will be more precise (because they could have changed in the meanwhile and because the whole team is more mature and expert of the problem domain) and would require less documentation, due to the shortest release cycle.
Unfortunately, there are some preconditions that make this magic happen. One is the availability of a domain expert. It's a key factor in many agile processes (not to mention the XP "cohabitation") but really reads like a simple thing, in a book. In reality one might not be that lucky. Domain experts might not be so available (I agree with you that this is a business suicide – don't get me wrong), or not so expert, or maybe simply do not have the right perspective. Well …these are basically the reasons why the analyst role has been invented. Forget what we've seen in the "Rose years" where an analyst was a man who produced useless diagrams. An analyst is a knowledge cruncher (this definition comes from the DDD book): somebody that becomes able to master the domain like the domain experts do (or possibly better) and to derive a model from fragments of information.
Many times, User stories are seen as a way to leapfrog the analysis phase and the analyst altogether. A good design will "emerge" as a result of iterations. Well, …the use case of Interlude 3 was one iteration. But if requirements were collected by developers straight from domain experts (as in Interlude 1) the result could just let you completely stuck with crappy code for ages. Many teams do not suffer so much from this limitation. Maybe they have rare beasts like developers with brilliant analysis skills, or the analysts really embraced the agile mindset and perfectly fitted in this role. Sometimes, instead, the analyst is perceived like "the person who writes the specs", and since the specs are not that necessary anymore, so is the analyst.
Hmmm … stormy weather approaching.