Apple Open Sources Snow Leopard's Grand Central Dispatch (Apple Insider)

Well, that isn't the only problem it appears to be trying to solve.

From what I can see, there seems to be four things in play here:

1. Systemic scheduling of threads for absolute maximum throughput, largely disregarding latency;
2. Thread re-use on a platform that finds them expensive to create;
3. Very, very easy integration of multicore processing into formerly single-threaded applications. This is a critical feature; with a few lines of special wrapping code, using blocks, programmers can do batch threading with little additional effort.
4. Very broad scalability. The whole concept of sharing CPUs may just go away as we keep adding more and more. At the rate things are going, we're going to have desktops with 256 cores within 10 years. If you have 256 full speed CPUs, why on earth would you even share most of them? The whole concept of a scheduler is probably going to need to be rethought soon, and GCD would appear to be one early attempt.