The fish tank heater has been an absolutely amazing success. The biggest problem we've encountered is the Winter Squash seeds germinated so violently that I had to transplant them into larger containers after just five days. Nearly everything has germinated by day five, with a couple empty cells that might just be duds or germinating at a slower pace.
I don't think any of my pictures demonstrates the effectiveness of the heating better than this picture of our cucumber seedlings. The heater is on the right hand side of the water reservoir, and the lack of water circulation means that side of the tank is hotter and the soil above is also a degree or two hotter on the right. This lead to the seedlings sprouting to form a 'more bars' commercial picture. This pattern was reflected in the Brandywine tomato seedlings as well. The next improvement would be something to circulate the water to keep the heating more even.
Winter Squash Day 3
Winter Squash Day 4
Winter Squash Day 5
Winter Squash Day 6