I screwed up by transplanting my tomato seedlings too soon. And I tried to cheap out by using poor quality potting soil. The seedlings haven't grown at all since I moved them to the larger pots a week ago, and they look a sickly yellow-green. Live and learn what you can't get away with.
I'm starting over and planted 24 seed cells with tomato seeds this morning, 3 varieties, three seeds in each cell. I'll thin each to the best plant. They'll be small when I put them in the garden in June, but I think they'll do OK.