By the numbers: airline industry wide statistics (and here with charts) for late arrivals, late departures, cancellations, etc. Looks like the industry average is about 20% late arrivals per year over the past decade. Unfortunately this table does not give times, like average time delay.

More: some airline consumer protection reports that have a wealth of information: Flight Delays, Mishandled Baggage, Oversales, Consumer Complaints, Customer Service Reports to the Dept. of Homeland Security, Airline Animal Incident Reports - Broken down by airline (the flight delays are even broken down by airport, flight route) over the past several years.