I use Confluence for sales support as an extranet, where I publish pages that can be viewed by anonymous users. Sometimes with permissioning to specific sets of customers. They don t need to have individual logins. A collective login and password may be enough. If I want to interact with them relative to a specific content (means, it s a content-centric interaction), then I ask them to use comments on Confluence. If the interactions are related to some opportunity or pre-sale, then I call them to interact on Salesforce Chatter.
Now, although I haven t experimented yet, I believe that a great integration would be to publish Salesforce reports on a Confluence page, so that users of the reports don t need individual SF licences and can view them (and comment them) on Confluence. Does it make sense for you?