On your dashboard you find 'Visitors statistics'. Here you can see how many people shared their photo online that day. These numbers are based on how many people shared their photo online through your GoPhoto - Photo Website. The actual amount will always be higher because people download their photo from your Photo Website and post them online their-selfs as well.
Statistics - System
When you want to see an overview of how many people shared their photo online over a different period of time go to 'Statistics' - 'System' in the sidebar.
You can change the date and get an overview over a different period of time. You can view these statistics daily, weekly, monthly or yearly.