Had a driveway poured in July 2011. Even though we used concrete with Ultra 500 fiber, 4 inches thick, numerous expansion joints and heavy road base, cracks began the first winter.

We live in Northern Calif. so it does occasionally freeze. But night time temps rarely fall below 30 degrees. Weather here is fairly temperate here year round.

The concrete provider is blaming these numerous cracks (20 or more with more developing) and concrete break off to "ground slipage". This sounds like a "cop out" to me that we can't disprove. We live on a hill where no other properties run off onto ours and have been here 27 yrs. Previously had black top driveway that did not crack.

I thought this Ultra 500 was supposed to prevent cracking!

You should be able to see them, I can see mine if you lay down on the floor and lay a flashlight on the floor so the beam is parallel. Looks like fine fuzzy threads.

I can believe that the fiber is there, and the ground slipped or froze or both. You don't say what measures you took to deal with freezing below the concrete. It seems to me that a driveway contractor should be aware of all this and should advise you before doing the job, but if you just hired him without a soil engineering, you are pretty much out of luck. I tore my hair out reading all the blogs about monolithic slab problems (and other kinds too) that I want for a garage in New England. As many theories as there are people.

My experience is in inspection of highway and bridge construction. We used four inch concrete for sidewalks and if they were to be traffic bearing our standard was 6 inch with wire mesh reinforcement. So I think that 4 inches for a driveway is cutting it pretty close even with fiber reinforcement which is good technology, but it can perform well only if properly designed (concrete and base material designed for the anticipated load), placed, and cured,
What kinds of loads have been on the driveway in that year it has been in service? It only takes one heavy truck to cause damage.
You thought right that fiber reinforcement is supposed to prevent cracking. But it won't overcome other possible deficiencies such as too high a water-cement ratio, improper curing, and numerous other possibilities.
Did you add a stone base or use the base that was there for the asphalt driveway? What kind of distress was present in the asphalt that was replaced? Any alligator cracking?
Slippage sounds like a pretty lame excuse and there should be other evidence such as open gaps.
If you can't see any fibers, you can probably have a sample tested at a lab. That is about the only chance for getting any real evidence with which to hold the supplier responsible.