I point you to the notes of D.C. Nanog, particularily the Sprint discussion.
http://www.academ.com/nanog/may1996/sprintlink.html#Notes
I don't remember for certain the figures that Jim showed on the detailed
map of Sprint's National backbone, but I do recall a 90%+ utilization
figure on mae-east and mae-west links by Sprint. I'm sure many others are
very near that as well. Don't mean to pick on Sprint, but they made that
information public at NANOG D.C.
I have no idea what the "intentions" are of the "big players". Don't even
want to get into that, as the only people that know the real intentions, are
those making the decisions not to upgrade their links.
What is fact is: the IXPs are not over utilized.. the links of the carriers
entering the IXPs are.
ROb