3D procedural noise is definitely a really great idea for compressing the size of a model and for real time graphics. One example of 3D procedural noise is Perlin noise, which involves computing a bunch of random gradients and other steps. This actually won Ken Perlin the Academy Award in 1997!
Followup on the above comment, Perlin noise is really great, and has a lot of applications in games with real-time graphics and random map generation. I've used it for terrain generation and it produces interesting results.