CPH,
I have never personally owned a set, but I will go throught the list of people I know who had had them replaced, some under the prorated warranty, and some under the extra tire warranty offered at the tire dealer, and some at their expense.
My father is on his third set of Coopers on my Moms minivan. The prior two sets were replaced for a nominal fee under the pro-rated tire warranty. Both sets had less than 20,000 miles and less than 1 year on them. The sidewalls were cracking.
Father tried a set of STE's (I think) on his Chevy 2500 4x4 gasser. After 500 miles he took them back to the dealer because they rode like #$%^$%, and took a ton of weight to rebalance. After another 500 miles the dealer bought them back and put on some Dunlops, and 25,000 miles later he is still happy.
Friend has a set of the new style AT's on his truck (1500, V6, 4x4, Chevy gasser). At 18,000 miles they almost look finished. About 1/3 of those miles are highway miles.
Friend had a set of the old AT's and had the sidewall blow out while driving down the highway.
Friend had a set of old style AT's and they would never balance right. Then had one replaced for broken belts. Then at 30,000 miles he junked them because they wouldn't balance and rode like #$!) He put on BFG A/T's and they balanced with little weight and rode beautifully.
I understand other experiences are different than the one listed above, but I have never heard of this many problems realted to one tire company (except Firestone

). For these reasons I will never buy a set of Coopers. For those of you that have them, good luck and I'm glad they are working for you.
-Ryan