Andrew, that's correct, you'd need to use a command line like that to grant yourself access to all mailboxes.
Hotfix, v-9 is correct. You can't use ExFolders in a pure 2007 environment. You have to have at least one 2010 server to use ExFolders. Thus, PFDAVAdmin is your only choice.
Petri, PFDAVAdmin does not behave as a normal client when accessing public folders. It goes through the ExAdmin virtual directory, which means it uses admin permissions, not client permissions. So you do not need to have a user assign you permissions on a folder in order to access that folder with PFDAVAdmin. You do, however, need to be an Exchange Administrator.
Paul, CDubb88, and Giuliano, so far I have not been able to reproduce the problem with the Everyone group. I'm able to browse for it and add it and I get no error. Can one of you email me at exfolders at live.com so I can get some more information? Thanks.