I think my three in-ground tomato plants have blight. I've never seen this in person before, but I know it's not uncommon in this country. It has been a long, warm summer, and has lately become a little cooler and more humid: good conditions for blight, I understand.
Although I'm not 100% sure of my diagnosis, apparently there isn't a treatment for blight, organic or not: plants must be pulled up and burnt. If allowed to remain, the fruit will spoil quickly; so just in case, they're coming up and I'll rescue the green tomatoes to make some salsa and/or relish. It's unlikely the fruit will have time to ripen now anyway, nearing the end of September, and luckily I have a good recipe for green tomato relish (from The Joy of Cooking).
It looks like my container tomato plants are still untouched, so they can remain for now. I'm glad, as the biggest one has been giving me big ripe tomatoes for a week or so now. I've made a point of saving seeds from it too--all of this year's plants are from my own saved seed.
As far as my remaining potato plant goes, I've no idea if it's got it too; it's hiding behind a mass of runner beans and I can't even see it any more. I won't be too disappointed if it has: it was a volunteer, and we don't eat many potatoes anyway.