From 1998 to 2006 there were ~21,565,900,000 (1) DVDs shipped out in North America. Based on the difference in volume between the two kinds of cases this equals ~888,000,000gal of wasted space. This is equivalent to ~1370 Olympic swimming pools!
See what happens when I get board.
References
1. http://www.dvdinformation.com/industryData/index.cfm
accessed 02/04/2008
I have no idea how accurate this information is.
[EDIT_21:54]
Since I'm in such a mathy mood. Here's some more random math for you.
Exxon Mobil reported Friday that it beat its own record for the highest profits ever recorded by any company, $40.6 billion. That means Exxon made more than $1,287 of profit for every second of 2007.
Source: New York Times