GTD, no joke about Schmoe overdosing people with the milk. The first time I had it, he dosed me so hard I was writhing on the floor, speaking in tongues, tripping the *fuck* out. I learned new respect for the cannabis plant that night, I'll tell you that for sure.
Some friends and I have been making milk using Joe's recipe for some time now and we've made some tweaks. The biggest is to use some lecithin, liquid form if you can find it, maybe 1tsp/gallon of milk as an emulsifier. It halves the time you need to cook the milk in the pressure cooker, which is good because it comes out a lighter, more attractive color while retaining potency.
I've found also that after you put the lid on, you want to keep your burners absolutely as low as you can. It's easier on an electric rangetop than on a gas stove where finding the balance between super-low and the slightest gust will blow out your flame is really tricky. According to a friend who said she heard it from Joe, he said that if you see any scorching happening at the bottom of your pressure cooker, either the temp. is too high or you're cooking it too long. I've never been able to completely eliminate scorching on my milk but I have found that using less material will help a lot at the cost of potency.
Higher quality material will produce lighter colors and less bitter flavor, but I don't really care about the flavor: I don't like it either which way. I usually just fill with leaf trim to full saturation and let it cook. The milk comes out bitter and dark but plenty potent and I pinch my nose and chase it with OJ anyway. I've even used trim that'd been through a kief tumbler to fine success before. Even then, I was dosing between ½-1oz and dosing lightweights at or under 1-2tsp (I err low, don't want to do to others what Joe did to me ;) ). "Do you want to smoke?" "No." "Gooooooood" :cool
Another tip: here in CA I buy Strauss Family Creamery brand whole milk. It's non-homogenized and still has cream that'll rise to the top. More fat = better.