I have to say I'm not really a fan of the secret recipes. For UUM, for example, I know how I would discover the recipes if I wanted to do so legitimately: make 9 UUM and then sit around for an hour or three placing all 511 possible layouts into a crafting grid. To me, that doesn't feel like "discovering a mysterious and hidden world", it just feels like a lot of pointless boredom, sore fingers, and wear-and-tear on a mouse button. So instead I decompiled the classes and read the recipes out, recording them in a web page (the address of which I will not share here). I could also have used a recipe book mod, but it would have been just as much cheating and I'd have to find and install a suitable one.
To me, the fun is learning about what all the tools do and thinking of interesting ways to use them to build neat stuff, not blindly dumping things in crafting tables hoping something will fall out.