Ian,
Is there any legitimate way to allow this? We're starting our rollout, but so far we've reserved public folders for reporting objects that have been promoted, not user generated content that hasn't been validated. However, the users would like to share the workspace with some of their coworkers.
In the old world they would have used excel and placed the file on sharepoint for the other users to open and refresh. We trying to remove excel from the workflow for all but the most complicated adhoc style reporting. It's difficult though because of these types of restrictions.