1.6 Geocode Requests. There is a limit of 50,000 geocode requests per day per Maps API key. This translates to roughly one geocode request every 1.73 seconds. If you exceed this 24-hour limit, the Maps API geocoder may stop working for you temporarily. If you continue to abuse this limit, your access to the Maps API geocoder may be blocked permanently.
With the new restriction, users with popular mashups that rely on this feature could start experiencing outages -- and they may even get blocked without purposely abusing the system.
How many people will this actually affect? I don't know, but it would be interesting to hear from you if you think this could be a problem. With all this API stuff happening lately, maybe Google's next move will be to disable the maps API altogether (yes, this is sarcasm, but who saw the Search API discontinuation coming?)
"The geocoder limit is actually not new. Ever since we launched the geocoder in June 2006, we've restricted access to 50,000 requests per day while we evaluate the performance of the service."