I'm reasonably certain it's late blight. Zone 7, northern Virginia. I've been watching everyone else's tomatoes drop like flies, and with the weird weather, I figured mine were next. This leaf damage was not there last night when I checked the plants. I found black/grey shriveled leaves on this Beefsteak plant this morning, with a little grayish-something-or-other on the bottom. The plant deteriorated rather rapidly, and has been kinda 'funky' for a couple days. I went away on vacation, and had a friend watch/water my plants. I came back, and the tomatoes were half-dead.
I wasn't going to sit around and wait for it to get worse, and take the rest of my plants with it. I went ahead and pulled it out and bagged it. Did I do the right thing by just taking it out, or was I overreacting - I wonder. I hope this doesn't happen to anyone else, it is rather disheartening.
Here's to hoping the remaining four plants are okay.