For several months I would try to open Outlook 2010 and nothing would happen. When I checked the Task Manager I would see two Outlook.exe processes running. If I killed the process with the most memory, Outlook would open and all would be well.
One day I decided to fix the problem. My first guess was that Outlook was not starting correctly. When I searched for "Outlook startup problems", I didn't find anything useful. After a little research I found that when I closed Outlook, the process did not go away. A quick search for "Outlook shutdown problems" immediately returned the most common problem is a third party Add-Ins. When I checked the list of Outlook Add-Ins, the most likely suspect was "Outlook Change Notifier" that was in an Apple subdirectory. I removed the Add-In and Outlook would open and close like a champ. [more]
I found a forum discussion, http://www.eggheadcafe.com/software/aspnet/32169731/itunes-outlook-addin.aspx, that said opening iTunes will reinstall the add-in. It tried it and iTunes acted like it was reinstalling and the Outlook Add-In was back.
Instead of removing the Add-In, just uncheck the box next to the Add-In to disable it. This will allow Outlook to close correctly and iTunes won't try to reinstall it. An alternative method is to rename the file that contains the Add-In: http://support.apple.com/kb/TS3500. Although Apple claims it's not a problem with Outlook 2010, it is.