As many of you discovered and pointed out, there is a bug in the Exchange Connector 3.0 RTM that is related to extending the work item classes data model with custom properties. For example, this could happen when you import the Send Email MP which extends the incident class. When this happens, the impacted work item will not be updated and you will see an event like this in the Operations Manager event log:
Exchange Connector: Unable to process mail item. Subject="xxxxxxxxxxxxx ID: [IR###]", Error Message=The key value of an object cannot be changed.
A fix is available for this issue now by calling Microsoft support and creating a case. We encourage you to only use this approach if it is absolutely necessary. A new build of the Exchange Connector 3.0 with this fix will be available in 1-2 months and will be available for download without creating a support case. That will be much faster/easier if you can wait for that.
Thank you for your patience and helping us identify this issue!