GPU Map Reduce
cse.ust.hk
cse.ust.hk
There is a lot of challenges of programming CUDA (disclosure: this is what my ongoing MS thesis work is on), but their code examples show they add no abstraction layer and because of the generality they force on their kernels (all must have the same signature) will be near impossible to reach full GPU performance.
tl;dr Unlike MapReduce, this does not make programming GPUs easier or accessing their hardware potential easier.