I've certainly learned a lot by getting over the barrier of purchasing a scale and mixing my own. I have Anchell's _Darkroom Cookbook_ and just recently bought v. 1 of Grant Haist's _Modern Photographic Processing_, which is the source of many formulas in less technical manuals and more, and I've also picked up others from various spots on the net like unblinkingeye.com, apug of course, the B&W forums on photo.net, and http://www.jackspcs.com/

Formulas I use regularly are ABC pyro, PMK, and Michael Smith's amidol formulas for Azo and for enlarging papers.

I've been experimenting with variations on XR-1, which is a developer for push processing and a few other applications like night photography. The next one I want to try is RAF pyro-metol high energy film developer.

For me it doesn't really pay to mix my own fixer. I can buy TF-4 off the shelf at B&H for the same price as Formulary minus the shipping but plus the sales tax, and I've worked out that I wouldn't really save much by mixing TF-3.