Marcus blogged about using ATDD in projects of rewriting legacy applications. He describes the problem of missing business involvement in those kind of projects.
He describes a possible approach for a project like this and a technical setup how to bind formalized examples (scenarios) to the new application.
What I miss in his explanations is any advice how to get from the legacy application to the formalized examples (scenarios). In my experience that is a very important aspect and I am afraid that many developers ignore or underestimate the importance of this for the whole BDD process!
Finding the relevant examples, formalize them in a maintainable way that can drive the development process and formulating them in a business readable language is is a lot of work and has to be justified and has also to be made transparent to stakeholders.
I would ask: Is the business involved in this process at all? Is any stakeholder except the developers interested in those examples at all?
If the answer to those questions is 'no', I am not sure if it makes sense to take the effort to go for scenarios in a business readable format. (note that I still think formalized examples do make sense, but not in a business readable format)
The real value of business readable examples lies in the discussions between stakeholders they provide a base for. They should be the baseline for prioritizing and re-thinking the functionality of the application. If there is no chance of involving business, they loose pretty much all of their value.
Business readable examples have to be an artifact that business cares about! Else there is the imminent risk that the whole BDD effort degrades to a petty effort of over-eager developers (I have been one of those, believe me).