So I turned to Google. A number of searches yielded little new info, but finally I hit upon this post on how to make perfect cream cheese frosting from How to Eat a Cupcake. Interesting: it suggests that cold cream cheese, not softened or room temp, is the way to go. Even more interesting: a comment from a reader about the method used at their bakery. Rather than creaming the cream cheese and butter, then adding the powdered sugar, Pinky said they cream the butter and the sifted powdered sugar, then add the cream cheese, in chunks. Beat, and add vanilla to taste. The end result is thick enough to pipe, which is exactly what I want. Best yet, it's not so sickly sweet that you can't taste the cream cheese, and you can use full-fat cream cheese, Neufchatel, or a mix.
I don't know how to explain it scientifically, but it works like a dream and tastes great. I took advice from the post and used cold cream cheese, and mine was smooth and lovely. Pinky broke down their proportions into home baking amounts, and here's the lowdown:
Pinky's Bakery's Cream Cheese Frosting
1 1/2 cups butter (3 sticks)
4 cups (16 ounces) powdered sugar, sifted after measuring
12 ounces cream cheese (full-fat, Neufchatel, or a mix)
vanilla to taste - about 1 teaspoon
Cream the butter and powdered sugar. Add the cream cheese, a chunk at a time, beating after each addition. (I didn't go crazy with the beating - just enough to work it in.) Add vanilla to taste. I actually added just a little more sugar to mine - maybe a few more ounces - to lighten it. I didn't want to risk using milk, cream, or sour cream to thin it. Delicious, and great with carrot cake!