Well, initially when I prepared the article, it was 50,000 hits per day. But I just checked now, and they have changed it to 5,000 hits per day . Their popularity must have gone up. Yes - 10 million would be a problem. But See the rate limiting area on this page......

http://developer.yahoo.com/maps/rest/V1/geocode.html

Also, the Terms of Use would probably restrict you from doing anything too high powered.