Despite experimenting with procedural worlds for years I only recently came across an excellent blog that I would heartily recommend anyone interested in this area takes a look at:
"Following one man's task of building a virtual world from the comfort of his pajamas. Discusses Procedural Terrain, Vegetation and Architecture generation. Also OpenCL, Voxels and Computer Graphics in general."
The breadth of task undertaken, the undeniable quality of the results and the fact that it's very much live and in progress make this one to watch for me.