Many people think that certain foods, like lasagna, many stews and hearty soups, tomato sauce and so forth taste better the next day. My question is, is that really true, and if so, why? The conventional answer is essentially, "the flavors marry", but that doesn't mean much. I asked this question on Dave Arnold's Cooking Issues podcast and he had some interesting answers but I'm curious to see what else this community will come up with.  
In the Good Eats episode "Stew Romance", Alton Brown says      See, as gelatin cools, it moves from a   suspended colloidal state to a gel   state, which if concentrated, can be   quite strong. [...] And that is why   our meat gets pretty hard when it   cools down. Now, what’s really   interesting, though, is that once   gelatin has reached the gel state, it   takes more heat to re-dissolve it than   it did to render it from collagen in   the first place. [...] Ahh, the meat   is perfectly heated through, but it’s   not falling apart. That’s because we   let it cool down before reheating, and   that is why stews, braises,   fricassees, and blanquettes are always   better the second day.   (Note that, as usual for Alton, his science is sound, but his other "facts" are to be taken with a huge grain of salt. For instance, the dish he makes that he calls Hungarian Goulash isn't Hungarian and isn't goulash. And the actual Hungarian stew that most Americans think is goulash is pörkölt. I haven't the foggiest idea where he got "pörkoft" from. Oh, and potatoes are very much a standard part of goulash, that's part of what distinguishes goulash from pörkölt.) 