I upgraded from Outlook 2007 to 2010. I create a Contact Group (Distribution List) in 2010 and enter an individual with more than one email address (because I want to send to more than one email) and when I save the Contact Group, all email address entries other than the default email address (i.e. Email 2, Email 3) disappear from the Group. This did not happen in Outlook 2007, where every email that I entered was retained.
Now, if I have an individual with more than one email address, and I use the Contact Group, I have to enter that individual's second address manually. For one person, that's not a big deal, but this is happening to many multiple email address individuals and in many Contact Groups.