Exchange Folder Permissions - query users access to all calendars

I'm trying to get a script working without any success which I'm hoping someone will already have a similar one for I could take.

Basically it needs to run a command like get-mailboxfolderpermissions -identity user:\calendar -user username >> c:\results.text

Basically I need it to check all accounts in the exchange server for a specific account with permissions over its calendar. So in essence check all folder calendar permissions for all mailboxes and if it matches -user, then wrote back to a file the calendar samaccountname they have access to.

Seems long winded but the only way in outlook 2010 to check what permissions a user has over all other calendars that are not provided via full access or inherited permissions.

Ideas appreciated.

Thanks