I'm not sure what you mean by "auto-approve" - There are plugins for things like wordpress which will junk comments automatically, solely on the result of the test, but others are more fine-grained. (The API does allow whitelisting/blacklisting by IP, etc.)

The success rate is pretty fluid but about 80% of comments submitted were judged to be spam today. Whether there are too many false negatives/positives is hard for me to say ..