well.. while I think Mr. Redmond is far superior to me in this respect, I must politely disagree. It does work in 5.5, the caveat being that messages must be sent 'directly' to public folders, not 'posted' to public folders. I have tested this on both platforms, and it works. While I don't have a URL for you, I do have some bullet points referencing the conditions that must be met for Journaling to work which I jotted down from Paul Robicheaux's excellent exchange book:
1- Messages sent to, or received by user mailboxes, including read receipts
2- Messages relayed through the IMS
3- Messages sent directly to public folders
But, you don't have to believe me, try it out and see.