Well, the only "old style" Omni I had was the Simonson Thor, printed on possibly the thickest paper of any collected edition I own, and it went "wavy" after about a week in my house. So, to some degree, have a couple of my paperback masterworks and, most severely, "Invaders Classics" volumes 1-3 (I didn't bother with #4). I'm reasonably certain this is due to humidity in the house.

I have two of the new "thin paper" omni's, the Michelinie-Layton Iron Man and (just recently here) Amazing Spider-Man #1, and so far there's been no sign of page curl. So in my case, I like the new paper not only for the reasons stated earlier in the thread, but also because (contrary to the experience of others here) it actually seems more resistant to curling. Go figure.