One of the best utilities ever created for Exchange is EXMerge. You can get the latest version of this tool here, where it is listed as the Mailbox Merge Wizard: http://www.microsoft.com/exchan...
Updated Jul 01, 2019
Version 2.0
Blog Post
Thanks for clarifying Mike - much appreciated. I clearly see that de-duplicating and maintenance of single instance are two separate concepts.
A thing of note on single instance is that in general I'd agree that mature stores do tend to approach 1:1 in the real world, but there are cases where your user habits will reflect your organisational culture. An example of where this comes into play with single instance ratios is within law firms that don't apply mailbox quotas. The combination of the lawyers' tendencies to store everything forever (ostensibly just in case), along with the tendency to do team-based work and share documents/revisions via email; is the reason that we see many Exchange stores in such places with si ratios approaching 3 or 4:1. These kinds of examples are surprisingly more common than I'd expected...just depends as you say, on your users habits.
Cheers
A thing of note on single instance is that in general I'd agree that mature stores do tend to approach 1:1 in the real world, but there are cases where your user habits will reflect your organisational culture. An example of where this comes into play with single instance ratios is within law firms that don't apply mailbox quotas. The combination of the lawyers' tendencies to store everything forever (ostensibly just in case), along with the tendency to do team-based work and share documents/revisions via email; is the reason that we see many Exchange stores in such places with si ratios approaching 3 or 4:1. These kinds of examples are surprisingly more common than I'd expected...just depends as you say, on your users habits.
Cheers