I installed my Sulastics in July 2008, along with my cognito leveling kit, dual 5100's and 1 inch blocks and 5100's in the back. After 4 years and 40 000kms of rough Canadian Roads, and Rig/Forest Roads, the Sulastics separated (in 3 places per shackle). The warranty as I understand it, is for 3 years on the rubber, 5 years on the steel.
That being said, having them on the truck was a dream, since during this period I wasn't hauling much in the bed of the truck (normally have 2-3K lbs of equipment) so they helped a ton. Definitely worth the price, and I will purchase another set if I go back to running empty (running stock shackles with Energy Suspension Bushings right now, with 2-3K in the bed 85% of the time).
I think what killed them, was the -40'c winters. These temps seemed to destroy my 5100's (Shocks and the Bushings), along with the overly rough roads. If you live in a warmer climate, I could see getting allot more life out of them.