[tsahyt]

No specific examples, but all of my best optimizations as in biggest-speedup were of algorithmic nature that actually improved asymptotic complexity.

In terms of my favorite ones, it's probably a piece of C code using SSE intrinsics to speed up intersection checking for a voxel raytracer I've been playing with last summer. After about 1.5 days of hacking I've managed to shave about 50% off the rendering time per frame. Nice learning experience but completely pointless in the end. Since it was still way too slow for any practical use, I started rewriting it and eventually stopped halfway through.