We've taken a two pronged approach where the BA will create a functional overview that is meant for the business and our people as a primer. After that are the functional details which are broken into definitions, business justification (as a developer you have to drink a bit of the kool-aid once in a while to get behind a project) and use cases. I created these docs, but our Director still insists on the use cases being in outline form and not simple note cards. I then churn those into technical use cases for us to work from while still using the functional details for business rules in the use cases.
In short...don't do what we do. Create a Word doc that has the business position for the solution as well as the definitions and terminology needed in the project. Make the use cases simple, even if they add up to 100+.
Once we have the use cases they are listed on a white board and assigned out...no formal system is used at that point but we have meetings (I wouldn't go so far as to say scrums) every other day.