Finding unused Public folders in Exchange
I saw this tip about how to find out when a public folder was last accessed in Exchange which may be useful if you're trying to rationalise your folders during an upgrade or migration. There is a WMI class called Exchange_PublicFolder which has a property called LastAccessTime which you can use. The only challenge would be if you have an anti Virus solution which scanned the Public folder, as you would not be able to tall if the folder was accessed by a user, or by an automated anti-virus scan engine.
Check here for the WMI reference documentation.