I've had some recent seed starting conversations with my good gardening friend Joe Lamp'l, which are available as a pair (part 1 and part 2) of podcasts on his wonderful joe gardener website. I've also received many questions on email, Instagram, Twitter and Facebook about the dense planting applicability to other crops.
Let's make this blog short on words and long on pictures. By the way, the answer is YES! Check out the following pictures:
A cell of tomato seedlings, from 2008
Beets, chard, and Asian greens, from 2010
Lettuce and some basil on the left edge from 2008
Peppers and eggplant in 2007
Basil in 2008
close up view of lettuce in 2009
closer look at peppers in 2010
So - yes - I use this method for: tomatoes, peppers, eggplant - and, beets, lettuce, Asian greens, many herbs, leeks, many flowers. It is a huge space saver - just a great efficiency tool. And....development of a love of transplanting is a must!