Re: Making Your Own Buttermilk
Whenever I need buttermilk I usually just buy a quart (or smaller if they sell the 500ml) - any leftovers I use to make Mile High Pancakes or Cornbread.
I have never made my own buttermilk...well actually I have, as I have made my own butter before and the milk that is left behind after the butter has been churned is technically "true buttermilk".
I have to say, you are right about how many different and conflicting stories there are about how to make your own buttermilk. Here is some of the helpful things that I read.
Harold McGee talks about "cultured buttermilk". Apparently this one is made by giving skim or low-fat milk the standard yogurt heat treatment. While "Bulgarian buttermilk" is made by giving cream cultures the yogurt heat treatment. There are a few more differences but that's basically the short answer. Bulgarian buttermilk is generally richer, thicker and more tart than regular cultured buttermilk. Seems like this might be a lesson on Rouxbe down the road :-)
Here is another link to Wisegeeks were you will find a bit more information on buttermilk.
Hope this helps! Good Luck.