Yesterday, I tried using the /info method of the API to predict the time left until 10M questions on Stack Overflow. In the process, I found that the returned "questions per minute" value was always 2.7, day or night.
I understand that the data is cached and the rate is averaged over some period. But 2.7 questions per minute is 3888 questions per day, which is less than half of what Stack Overflow gets during a weekday. The question count returned by the same API method has been increasing at a much greater rate than 2.7. I suspect there is a bug in how this rate is computed.