"For most of our APIs there is no limit. For a handful of our APIs, for technical reasons, if you go beyond a certain threshold, we ask that you email us so that we can make sure we have enough servers to provide that capacity. But we haven't said no yet.
For example, for the Maps API, there are many very large web sites using it from the Boston Globe website to Yelp.com... These are all very large commercial businesses with very high traffic. So we don't formally have usage restrictions for any of our APIs that I'm aware of".