Recently I installed Office 2010 and was pleasantly surprised at how everything worked and how easy it migrated.  Then one day I went to open Outlook it started crashing unexpectedly, I found the following article which works for some people but did not work for me.

http://blogs.msdn.com/outlook/archive/2010/02/17/Outlook-Gets-Social-wit…

During my process of getting it backup and working, I had to do the following

Before looking online 

I performed a repair/reinstall

Perform the steps from the article above

Disabled the Add-In from the Options tab

Created a new profile and setup e-mail account again

Mail worked and the add-in was gone

For another user we actually had to removed 2010 and install 2007 then reconfigure the e-mail accounts again.

After that we were able upgrade 2010 and restore functionality for them.