With regards to East Lansing--I was there and the floor tickets were sold out. However, either the band or the stadium officials misjudged how many people could fit on the field comfortably, so only like 5000-6000 tickets were sold for floor GA. But the floor tickets were sold out on Ticketmaster and sold out as soon as they were put on sale for the public.
As for the seats there, from what I remember, most of the seats were full--especially once U2 took the stage. I want to say there were around 65,000 people in attendance that night, which is damn good for a concert in MI given the depressed economic state we've been in for the past 4 years. Here's an article about it and how the band had to shell out $250,000 for a new field for the Spartans: http://www.nesn.com/2011/06/u2-tears-up-spartan-stadium-field-will-pay-over-a-quarter-million-dollars-on-repairs.html
I would hope if U2 (or any other band) ever plays Spartan Stadium again, they'll make sure to sell more floor GA tickets since there was quite a bit of open space (which was good in a way, as we all had plenty of room to move around and enjoy a great show).