As a whole, if it was all added up, how much data does the internet transmit each second? Does anyone know of a source for this information? I'm just looking for a ballpark average.

Good question we will need to call Gore

Cisco has developed a forecast model to estimate future global IP traffic growth. Based on Cisco and independent analysts' forecasts, highlights include the following:

   * Global IP traffic will increase by a factor of five from 2008 to 2013, approaching 56 exabytes per month in 2013, compared to approximately 9 exabytes per month in 2008.
   * By 2013, annual global IP traffic will reach two-thirds of a zettabyte (673 exabytes). A zettabyte is a trillion gigabytes.
   * By 2013, the various forms of video (TV, VoD, Internet Video, and P2P) will exceed 90 percent of global consumer traffic.
   * By 2013, global online video will be 60 percent of consumer Internet traffic (up from 32 percent in 2009).
   * Mobile data traffic will roughly double each year from 2008 through 2013

Total international bandwidth capacity was roughly 25tbit/s for '09, average peak utilization was about 50% of that.  Good enough?  More info from Telegeography.  That was from the 'executive summary' PDF, full data... well you gotta pay for it, and I'm not.  

well, there are about 1.8 Billion internet users, figure 1.6Billion of them are downloading porn/mp3s or 'other'...  

There's no way to know.  Most of the traffic now goes through private peering points so any estimate would be a wild-guess at best.  It isn't like a decade ago when you could look at MAE east and west and use that as a good starting point for an estimate.  For example, at work we have 800Mbps total to other providers.  Only 1.5Mbps of that passes over a public phone lines.  The rest is mostly Ethernet to other providers in the same data center or to privately owned fiber running to our building from our data center.  So going by publicly available records, you would underestimate the amount of bandwidth we have by over a factor of a hundred.z

1 bazillion bazillobytes

Or hacking the pentagon from China.