I have a FGDB feature class which I deployed from ArcMap 10.1 as a Feature Service to ArcGIS Online for Orgs Hosted Services. I enabled 1) Editing (Add, Update, Delete) and 2) Track Edits. Feature Service is shared with the members of my organization.
The edit tracking works as expected when accessed from ArcGIS.com JavaScript map viewer; ArcGIS Explorer Online; and from ArcGIS iOS app. The CreationDate, Creator, EditDate, and Editor fields are populated as expected when viewed from these clients.
However, when I connect to the Feature Service from ArcMap 10.1, those same fields in the attribute table are not populated. The CreationDate and EditDate fields all default to 12:00:00 AM; the Creator and Editor field values are all NULL.
Interestingly, when I go to ArcGIS.com>MyContent>click on the Feature Service>export the layer to shapefile, the resulting shapefile attribute table does contain the CreationDate, Creator, EditDate, and Editor fields, and they are all populated with usernames and dates.
So there seems to be a bug when a hosted feature service is accessed with ArcMap 10.1. In that case the edit tracking fields are included in the attribute table, but they are not populated.