Would be cool to have a cryptography system where you can load values from a file into a texture on a OPENGL surface and apply different filters/transformations to the surface to generate a new image. The final image is the encrypted/decrypted file. Since modern GPU's have multiple pixel pipelines theoretically you can encrypt/decrypt messages quite fast. Kind of curious if the output image would be different from card to card (do to the way the OPENGL are implemented in the drivers). I believe people have already done something similar when generating rainbow tables. Just an idea for a crackme =).

Edit: Looks like if you google gpu crpytography you can find some cool papers.

For the record it has been somewhat suggested before, but with DX shaders... (no troll intended)
http://www.woodmann.com/forum/showthread.php?p=66973&postcount=14

If you come to do things on the subject, I (and the CRCEKL) are very interested, although sucking at crypto. =)