Well, I hope I'm not adding fuel to the fire here...
RichR's topic on this thread got me little interested about the subject. Back in June, I started my new collection with cactus mix prepared by the California Cactus Center. Here's a sample:
I don't know what's in the soil itself, although it's mixed with gravel and maybe some pumice. There also seems to be a little organic material, but I'd say not peat or any of the wood products I'd expect to see at Home Depot, Armstrong Garden Center, etc. From the CCC's advice, I add in extra pumice with 20% for Astrophytums, 25% for my Cephalocereus senilis, and 30% for my Melocactus matanzus. I also have 3 Turbs, which I'm considering for 20-25% additional pumice as well.
I'm not sure if this sample is going to give us any useful info, but I'd be curious. The CCC has been around for 30+ years, and while I hope that they know what they've been doing, I don't want to take anything for granted either. I'm always willing to consider different opinions. (By the way, the CCC didn't seem to be unusually expensive. However, I'd kinda see a 30 lb. bag go down the tubes if it turns out that I may have to go back to the drawing board for a better cactus mix. Sorry -- I hope I don't mean to hijack this thread!)