I realize you aren't trying to create a portfolio system I'm just interested in understanding both portfolio systems and what you are building better.
Portfolios are intersting because there is so much in OACS that is a lot like one yet we don't actually have the functionality.
For instance, in the Homework package a student uploads a document as evidence of having done an assignment. Then the instructor uploads comments. So far this is very similar to a portfolio system. But in a portfolio system there is a view of all of a student's work not just assignment by assignment and there is addional flexibility to control who has read on both the documents and the comments.
You're system will have the student centered view of assignemnts right?
Can you view a grade report by student across classes or just for all assignments within a class?
Does the instructor just submit a grade or can he also submit comments?
In your system, does a student submit a file storage document as thier assignment, this is the way the homework package works, or are assignments submitted through a more survey like interface?
I'm not trying to add any requirements, you have already bitten off plenty! Just trying to understand what you are doing and think about different ways the same functionality might be reframmed for marketing purposes. Maybe, if its somewhat close, the portfolio products might give you some UI ideas.