Google maps and geocoding functions have a request limit.
With Google Maps the limit is 25000 maps load per day, and is a limit that depends by your apikey
So if there are 25000 users and each user has made a request, you have exceeded the limit, and in your Google API Console you can see your quota for :
-Ad Exchange Buyer API
-AdSense Management API
-Analytics API
-Audit API
-Calendar API
-Google+ API
-Latitude API
-Static Maps API
-Street View Image API
-Translate API
-Identity Toolkit API
With Geocoding the limit is only 2500 request per day, and in my Google API Console there isn't showed a quota, Mean that the limit is related to the user IP and not to the developer certificate or I missing something!??