Click the mail icon next to your account name on the top of screen.
The default display is a summary of your recent activity. However, the time span's end date is later than the start date. (This might be timezone related.)
E.g. it's currently stating
2011-02-18 22:14:08Z to 2011-02-18 23:59:59Z
as the time span. (I'm GMT +11.)
Also note that 'today' (the default display) is not in bold.
Therefore, selecting the other menus (reputation, responses, favorites, revisions, and badges) all return nothing because of the incorrect timespan.
In practice, this can be rectified by clicking 'today'.