Great post Peter!
I've also been extremely confused about Schnauzer Bumps. Bisi is what my vet calls "cyst-prone" (not a technical term!). He has had several cysts that have popped and drained on their own. The smallest one started out about the size of a pea, and got a bit bigger before bursting. 2 of the others that have burst were a bit bigger to start out with. 3 of the 4 were there for years before bursting, and one I never even noticed he had, so I'm unsure of what size it was beforehand (though the wound it left afterwards was huge...it actually burst AT the vet of all things, so they shaved the area and cleaned it). He currently has two on his head that have been there for over a year...but those are coming out at his teeth cleaning in a couple of weeks. All of the ones that have drained on their own drained a brownish sticky fluid, followed by clear fluid. We have treated each one with hot compresses and antibiotics.
He also has two small, hard bumps on his head that do not feel anything at all like the cysts do. They are not squishy, and seem to be more a part of the skin rather than on it. My vet said these are likely schnauzer bumps.
Bisi will occasionally (once or twice a year) get small, red pus filled bumps on his tummy. These I believe are allergy-related, and eventually always crust over and go away within a few weeks.
And then we also have the benign tumor on his lower jaw. I can't remember what type it is (I was sooo relieved to find out it wasn't cancerous that I didn't think to write down the name of the thing when the vet called...I will call Monday and find out), but it is definitely a tumor and not a cyst. This, too, will be removed when we get his teeth cleaned.
So...overall, it seems that Bisi has practically every different type, size and shape of 'bump' possible!