The Events Tracer
module keeps a brief record of when things happen. If you wanted to understand how many files had been downloaded in the last couple of days then this is the module you want.
It also records:
jrCore_download_file - A user downloads a file
jrCore_stream_file - A user streams a file
jrUser_login_success - User logs into the system
jrUser_signup_activated - A new user activates their account
Which you can then use for whatever purpose you like.
The jrSolo skin uses this info in the /fan_activity.tpl template to show the last 10 actions performed by fans looking at the skin.