There's a guy on my team (of 12 people) in Apple that literally does nothing but screen bugs. I think he screened 100 bugs last week and there are still hundreds more unscreened. It's really hard to keep track of.
Other people are saying "Apple must get thousands of reports of dubious quality". If that's true I'd expect O(100) reports screened per day? I guess automated screening roots out lots of them?