Groups in Mail
Well, well, well. Another problem I discovered. Tried to email my group in my Contacts, and guess what. I can't. Used to be able to click on the name in the To: field in Mail to have it show me all the individual contacts, but now its just an editable 'word', not a group at all. What a piece of **** this upgrade is (excuse my language, but this is terrible).
iMac, OS X Mavericks (10.9)