I've been making a lot of yogurt lately using Anne Mendelson's super-easy recipe from Milk, and decided to run a test. I made one batch of yogurt with standard nonorganic whole milk and another with Straus unhomogenized organic milk, a local brand. Full disclosure: I am deeply attached to Straus, which comes in old-fashioned bottles with the cream on top and is incredibly expensive. I need any reason to justify buying it.
Interesting, watching the two milks heat in pans side by side as the supermarket milk was the shocking white of Elmer's glue while the Straus milk was a light buttery yellow.
My father came over shortly after the yogurt was finished, and we did a blind test. His answers were exactly the same as mine. Next to homemade yogurt, the commercial yogurt -- and this was a decent brand, Brown Cow -- was thin, sour, and basically lousy. The other two were almost identical, thick, creamy, and sweet-tart. There was a tiny bit more flavor to the Straus yogurt, but you really had to concentrate to detect it.
I can no longer justify Straus milk for yogurt making. But I do think that if you want to appreciate yogurt qua yogurt, you need to make your own. It's vastly better. On the other hand, if all you're going to do is put it in a cake or biscuits making yogurt is a waste of valuable time you could spend watching Gossip Girl or reading a good book.