Whether dealing with SF V1 or SF V2, if you are coding in ASP.NET, the session and session management is going to plan a pivotal role in your application.  However, in SF V2 we plan to have a true session manager that will clean things up a lot, but the main problem in SF V1 with the BO in the session has to do with the ADO.NET back end inside the BO.  You can prevent the data duplication issues that you mentioned in SF V1 if you manage the session correctly, but you have to create a static root object (BO) and the populate the instance objects.  So depending on what language you are using this might change slightly.