While doing my CRM Online install, I attempted to set the client up with the CRM Outlook client. It appeared to install properly but then Outlook would not run. When attempting to run it, we would get a message that the program had not shut down properly and the data file needed to be massaged. After a bit, Outlook would simply shut down. I eventually decided to uninstall the CRM client and full functionality was restored to Outlook. I also noticed that the customer had Microsoft Office Business Contact Manager (BCM) installed. Further research (asking my fellow MVPs) revealed that this is a common behavior. Matter of fact there is a hotfix in the works, but not public yet, to fix this. In the meantime I will simply uninstall BCM and then reinstall the CRM client.
One of the benefits of this 'research' was that a recent CRM Team blog, CRM 4 Outlook Client - Issues and Fixes, was highlighted that listed a number of hotfixes for the CRM Outlook client. It can be found here. I encourage you to visit this blog and learn about the fixes. Links are available to request the individual (free) hotfixes.