37,000 per day.
FAA statistics say there were 13,531,058 Air Carrier flights in 2008. I divided by 365 days. Probably less days which would mean more per day.

156,000 total flights per day. (56,823,081 total in 2008)

183,000 total flights per day based on the last 18 year average.

1,204,006,309 total operations since 1990.

That's because there are 10 million less flights per year now than 18 years ago due to gas prices. Most the loss is in general aviation or in other words guys who aren't paid to fly but do it for fun, for sport, because they love it. This is where our future pilots come from. If 10 million less flights means that many less pilots are being trained. The airlines are going to be faced with both a gas and pilot shortage over the next few decades.