Group customers for access rights

 It would be hugely helpful to be able to define types of "customers" and group them for purposes of access rights.  We use our support portal for pre-sales support, where they're technically a prospect, for ongoing maintenance & support, where they'd be a customer, and for our partners, which are neither, but still individuals we need to provide support to. As you can imagine, for each level - prospects, customers, and partners, they have access to increasingly more technically in-depth information.  Right now, for everything that I want customers to see, but not prospects, I have to list out all of our customers (which is an ever-increasing list) into the "Visible to" field. This is a big hassle and VERY error-prone.