"and if they care to share the techniques they use to create them from the basic texture map."

Well, if you painted the texture map from scratch and don't have to worry too much about burnt in specular, things will certainly go alot easier. Biggest problem I can see is eliminating lighting effects on the 2d map in order to create precise bump or displacement. In my case this would mostly be a concern with creating bump for close skin detail effects. Probably 100% painted maps are the most flexible route to go in particular for generating derivative greyscale maps... of course this is a tremendous amount of work and is probably best utilized for creature skins or alien, goth, cyborg, toon type skins for figures. Then you don't have to worry so much about the photorealism thing, i.e. people expect a pin-up character type skin to be derived from a merchant resource (as about 99.9% of them are), which in turn leads to the 3d.sk photoreference method. I'd say the toughest part of texture creation is double checking seams and cloning details and fudging to get things just right.

Don't discount the use of procedural methods and masks in combination with maps either... e.g. turbulence, granite, noise, spots, etc.

Another maybe obvious point would be to keep everything you create as separate layers, and I mean everything... including symmetry details. You'll end up with way more flexibility and can begin to create your own merchant resource as it were. Downside, gigantic .psd (or whatever) files...