Had to revive this thread, because last night I made my best batch of yogurt so far. It's the first time I added dry milk powder (fat free, instant).
I probably wouldn't have experimented, except I ran into a tremendous sale on the dry milk powder. I've never liked the taste of milk made from powder, so I wasn't sure how I'd like yogurt made with it.
I added a cup of dry milk to the milk and made as usual, and I was SHOCKED at the difference in both flavor and texture. Not only does it make a thick yogurt, the flavor is even milder, and sweeter than my normal batches. This is the first batch that I haven't wanted to sweeten at all!
I've also found a few shortcuts. I had been using the crockpot alone for heating the milk, and when starting with milk from the fridge, it takes about 12 hours to make yogurt (I don't really have to do much during those 12 hours, but I have to be home for the first 5 to 7 hours of it).
Now I heat the milk in the microwave before pouring it into the crockpot. Just a couple minutes per quart. It cuts about 4 hours off the yogurt-making time.