Our organization has a large set of public folders. How can I determine the size of the public folder hierarchy so that I can estimate the bandwidth effects of folder changes?

Each public folder database contains a copy of the hierarchy, so creating a new, empty public folders database will solve the problem (although you must be running Microsoft Exchange 2000 Server or later). Create a new public folder database, and don't add any folder replicas to it. Allow replication to finish, then examine the size of the new database. The size won't be exact because the file also contains some database overhead, but this method should give you a good estimate.