I do and I don't. I use whatever I have -- I don't buy special yogurt for a recipe (unless it is the recipe that CALLS for LEMON yogurt) and I don't add milk. I haven't noticed a difference.

Linnea, the banana bread recipe I use calls for 1/2 cup of sour cream, so that's what I always use. Obviously, Greek yogurt has less liquid since the liquid (whey) is drained out of it. For baking purposes, your question regarding adding milk made sense.

See if this (from Cook's Illustrated) might help when it comes to baking with yogurt...

"We weren’t surprised with our findings when we baked batches of bran muffins and peach cobbler (with a biscuit topping) using these two different types of yogurt. In both instances, the samples made with Greek yogurt tasted slightly drier than those made with American yogurt.

To come up with a formula to compensate for the difference in moisture content, we drained 1 cup each of plain whole-milk, low-fat, and fat-free yogurt in a fine-mesh strainer lined with cheesecloth; after two hours, 1/3 cup of liquid had been exuded from each sample. Armed with these results, we went back into the test kitchen, reducing the amount of Greek yogurt used in our recipes by one-third and making up the difference with water. The results? Tasters found the muffins and cobblers nearly identical.

So to substitute Greek-style yogurt for American-style yogurt in baked goods, remember this rule: Use only two-thirds of the amount of Greek yogurt called for in the recipe and make up the difference with water."

I would have said what Cholebud posted, though with less precision. Greek yoghurt is also a bit tangier/sourer. But then there's which kind of American style yoghurt, and what's the definition of that? Some are about the consistency of sour cream, some more like heavy cream, some in between. My favorite yoghurt and the one I'm more likely to have on hand is White Mountain "Bulgarian" yoghurt (from Texas), which is naturally cultured rather than being injected with a culture starter. It's natural yoghurt the way it used to be and no thicker than cream.

Like with any new ingredient or recipe, try it, adjust, try again. :)

I only stock greek yogurt so any recipe calling for milk, sour cream, etc, I just thin with water until I get the right consistency for a proper liquid measure.

Thanks, all! I normally have my own homemade whole milk yogurt, so this has never come up before. I use Fage or some other Greek yogurt for a starter, but that's just because I like the taste of that culture. I don't strain the one I culture. Too much work!