Qualcomm has said before and now they are saying again, that they won't have any quad core offerings until the end of the year. But when they do, it will be a 2.5 Ghz quad core Krait chip, along with their next-gen GPU platform called Adreno 3xx, so while the current dual core Krait is exciting, I think the quad core version will be a lot more exciting.
I don't think quad cores are extremely useful for anything but large tablets and hybrids like the Transformer Prime, or if you intend to use Ubuntu for Android. But the more important bit here is that it will reach 2.5 Ghz per core. Since most apps on any OS take advantage mainly of only one core, this matters a lot. Plus, Krait brings around 30% performance improvement over Cortex A9 and 60% improvement over their old Scorpion core.
This is interesting because it means most high-end chips in the market will be based on Cortex A9 (waiting to see what Tegra 4 will have though) and its main competition should be the dual core 2.5 Ghz Cortex A15 chips. If those bring significantly higher performance per core, then they would be preferable over the quad core Krait, just like today a dual core Krait is preferable over a quad core Cortex A9 chip.
Both Krait and Cortex A15, and soon Cortex A7 are very exciting technologies, and should make our devices both more energy efficient and also a lot more powerful than they are today, leading the way to replacing our laptops one day, either by docking a powerful phone with a PC monitor, or by using Transformer-like hybrids.