September saw more than 10.2 billion requests on the AdMob network. They also released a good article about how to put their statistics in context.

Top 5 Countries

   1. United States (47.3%, 0.8%)
   2. India (6.5%, 0.3%)
   3. Indonesia (4.7%, -0.8%)
   4. United Kingdom (3.4%, -0.7%)
   5. Philippines (3.1%, -0.7%)

Top 5 Worldwide Handsets

   1. Apple iPhone (16.9%, 0.3%)
   2. Apple iPod Touch (8.4%, -1.7%)
   3. HTC Dream (2.8%, 0.7%)
   4. Samsung R450 (2.5%, -0.3%)
   5. Palm Pre (2.0%, 0.5%)

Top 5 US Handsets

   1. Apple iPhone (18.9%, -0.8%)
   2. Apple iPod Touch (9.2%, -4.2%)
   3. HTC Dream (5.5%, 1.6%)
   4. Samsung R450 (5.3%, -0.7%)
   5. Palm Pre (4.1%, 1.0%)

Download the full report here: http://metrics.admob.com/2009/10/september-2009-mobile-metrics-report/