One thing CPUs can do much better than GPUs is the kind of "mining" described at http://devtome.com/doku.php?id=cpu_mining

There are quite a few currencies and other assets that have been running along those lines for years now, as shown at http://galaxies.mygamesonline.org/digitalisassets.html

Bear in mind that in addition to discouraging GPUs it is also necessary to make it hard for botnets to play too, otherwise instead of losing out to GPU farms ordinary users lose out to folks who run botnets.

Thus it is best for not only the code required to involve a whole lot of decisions and branches and different possibilities but also for there to be an advantage to users who are at their keybpard relatively frequently, so that trying to run hundreds or thousands of "mining processes" tends to take more and more actual human intervention to keep them all running and to keep them all adapting.

-MarkM-