I wonder how long it will be until we see gpus used for general purposes on the server- like accelerating apache or mysql. Since this hasn't been done yet, there must be some reason it's not possible?
MySQL is heavily disk-bound. It is not CPU-bound except for things like sorting multi-gigabyte datasets, which people rarely use MySQL for. For most purposes you're better off installing more RAM than offloading computations to the GPU, otherwise MySQL has to spend all its time waiting for the harddisk.
Also, there are block modes that are seekable and thus could be parallelized if you had a big enough backlog, CTR mode in particular, but parallelizing individual streams is not likely to reap big enough rewards to justify the complexity.
I was surprised to discover that GPUs can accelerate SQLite http://pbbakkum.com/db/ and routing http://shader.kaist.edu/packetshader/ (although you're probably better off using an NP for routing).