We do not currently use it because we are not allowed to permenantly delete anything. If it had the ability to export items to some kind of file system (PST or better), then we would start using it today.
Basically it boils down to the fact that we do too much legacy work and can never afford to throw anything away. Right now we are stuck with PST files using the autoarchive, huge mailboxes or huge public folders. None of these solutions are really valid for us.
We have tried dragging these out to a file folder, but explorer does not understand email message (you can't see sender information, etc) and it doesn't deal with duplicates properly (when dragging messages our of Outlook into an Explorer Window).
If we could add something in to Windows and tell it a folder is an "EMail" folder, then we could have the mailbox manager export all of the old, large, obsolete, etc messages out to the file server as .msg files (with a GUID in the file name so they are all unique). Windows Explorer would recognize the contents of the window (either automatically or because we told it to) as email message and it would display subject, sender, date/time sent, etc, rather than the normal information.
This should be fairly easy to do. It would be a HUGE benefit to us and make the mailbox manager a much more powerful tool. The messages would still look like messages, they would maintain the same folder structure they did inside of Outlook/Exchange, but it would take the burden off the exchange server.