From Minnesota Internet Traffic Studies (MINTS):

In spite of the widespread claims of continuing and even accelerating growth rates, Internet traffic growth appears to be decelerating. In the United States, there was a brief period of “Internet traffic doubling every 100 days” back in 1995-96, but already by 1997 growth subsided towards an approximate doubling every year, and more recently even that growth rate has declined towards 50-60% per year. South Korea, which along with Hong Kong appears to be the world champion in Internet traffic intensity, experienced its brief burst of “Internet traffic doubling every 100 days” around the year 2000, when broadband was widely deployed. It then appears to have had several years of annual traffic doubling, but currently (based on anecdotal evidence) is also growing at about 50% per year.

Traffic growth rates of 50% per year appear to only about offset technology advances, as transmission capacity available for a given price steadily increases. Thus although service providers are pushing to throttle customer traffic, an argument can be made that they should instead be encouraging more traffic and new applications, to fill the growing capacity of transmission links…

Interesting. But the MINTS researchers’ reservations about the reliability of their methodology makes one conclude that nobody really knows what’s happening.