Some small things that were updated.
Account Security option added – just a few old settings like Changing Password, removing your messenger password, changing LIVE IDs for your account, requiring password at sign-in and a Xbox LIVE pass code, just a move around of the UI.
Manage Exercise Info option added – this allows you to (optionally) tell Xbox the following: your height, weight, year of birth, and gender. Information for it says: “These attributes are used by Xbox and some Kinect games and apps to improve estimates of your exercise stats. Exercise stats include fitness scores from calorie burn, time played, physical intensity of movement, and feedback from physical activity.”
And an update to the text on the social tab that now has the text Avatar Store with a small icon beside it and a Sign In Or Out option. In regards to what Major Nelson said I can imagine it being for the new dashboard update as seen below.