This post is largely for future me. I'm fed up with (re)writing/(re)discovering some of these queries. However, I also hope it can help other people. This post was written specifically whilst I was finishing up with an Exchange 2010 installation. However, should work verbatim with 2007 and some of the queries may require a little alteration for 2013. If you're still on 2003. I'm sorry. So your Exchange server has a w3wp instance with high memory and cpu.
The important thing to remember is that in Exchange 2013 Public Folders don't really exist like they used to. They're basically mailboxes. In this particular scenario Public Folders were accessible internally, but not via Outlook Anywhere (or Outlook RPC over HTTPS if you're old). This problem can manifests where the email address policy that applies to the Public Folder mailbox does not assign an email address that can be configured by autodiscover.