Yes, I have used them, too, but I found that without warming the soil first, the tomato plants really don't grow very much. The wall o'water keeps them from freezing, but they don't grow that much faster than ones that were planted after the last frost.

how did it go?

Results are in line with what Blueheron said. The tomato survived just fine through some very chilly nights, but didn't grow perceptibly. It's growing now, but the ones I kept under the lights and put out on Mother's Day are now larger and stronger. I guess the only advantage I see of putting tomatoes out early is freeing up space on my light table.