I bought two walnut and country loaves from Tartine for a dinner party about a month ago. Of course, it was way too much. I froze about half and kept the rest in paper bags. The next day, both loaves were very good. The crusts lost something, but my wife and I actually agreed that the insides were better, something about the wait made the loaves more firm and the yeasty taste was stronger. Two days later, they were actually still soft, but the crusts were starting to fade. Three days later, still edible, the fermenty yeasty taste was still there. As you might expect, the walnut loaf does better, since it's more dense.
I just tried the frozen loaves yesterday. The crusts did a lot better than I had expected (the bottoms still have a good crack to them), but the bread was a little chewier than I expected. Again, the walnut bread did better than the sour. Definitely better to let the bread sit out and eat it over a few days than to try to freeze it. I had wrapped them in foil and then in baggies, maybe that was a mistake?