I've done it.
After about four and a half years of on-again-off-again experimentation, I've finally gotten my homemade cold brew coffee to taste really good. For the longest time, I was making batch after batch, and it just did not taste good. So now that I've finally got the process down, I'd like to share.
I start with 3/4 cup of coarse-ground coffee grounds. None of this by-the-pound garbage. Are people supposed to set up a scale in their kitchen? I buy the big huge bag of Starbucks beans from BJ's wholesale club and grind them coarse. Then I dump them into the french press. I don't know how many ounces of water that holds, but I'd imagine that a french press is fairly standard size. Fill it up with water, (I use tap water) give it a quick stir to make sure things are mixed, and let it sit on the countertop for 12 hours. Not in the fridge.
When the 12 hours is done, press the grounds down and pour out what you've got into a container of some sort. Here's the part I'd been doing wrong for so long, and why it had always tasted like crap. You now have to dilute it. A lot. I've seen lots of recommendations for 50% water, but I tend to do something closer to 60% water. And it still tastes strong. If you like cream or milk, add that, and you're good to go. If you like sugar you're going to have a harder time since sugar tends not to mix well unless you've got hot coffee to melt it.