According to the EU Trademarks & Design Registration Office (OAMI), Microsoft filed a trademark for Xbox Now (without the exclamation mark) in October 2012 - it's stated to be related to ''Audio, video and multimedia broadcasting via the internet.''
I think the rumors of Xbox Next being called Xbox Now! were confused, maybe this is actually a service to rival PS4's Share button, and involves uploading/streaming video clips via the internet - also trademarked around the same time were Xbox Fitness, Xbox Sport, Xbox Music, Xbox Video, and Xbox Games. Microsoft also apparently filed a trademark a week ago for game software called [FUN]ction.
Guess we'll find out tomorrow.