Hoop houses start being very useful in the fall. You can cover the hoops with fabric as the weather starts to get cold, protecting your tomatoes from light frost, and keeping them nice and toasty. Sometimes, we have a frost in early October, and then it can be fairly warm right up through December. This method will save your plants.
In the fall, you can start planting spinach, swiss chard, bok choy, broccoli, cabbage, carrots, lettuce, and anything else that can stand the cold.
I use one layer of fabric in the fall, then as it starts to get very cold, or when we are going to get snow, I add a layer of plastic. This brings the climate of my garden from Massachusetts, to the equivalent of Georgia.
This is the fabric I used: http://www.johnnyseeds.com/p-5452-agribon-ag-19-83-x-50.aspx
This is the plastic I used: http://www.johnnyseeds.com/p-7709-tufflite-nursery-clear-greenhouse-film-10-x-100-roll.aspx
For the winter, I made two large hoop houses, each one covering three beds. This was easier, than individually wrapping each house. There are several ways to secure the fabric and plastic. They sell plastic clips. They work okay, but they tend to tear the fabric, and they tend to break, and get lost. I find they work best on the ends of the rows. putting spare wood and fence posts worked the best to keep the fabric down. I would put them on top of the fabric on the ground, and push them right up to the beds.
When everything freezes, it stays in place. Nothing keeps the plastic secure like feet of ice and snow.
In the spring, I used extra hoops, (the wonky ones) and rested them over the houses. That helped keep the fabric from blowing around too much.
Now, plants do not grow quickly during the winter, I was able to harvest chard, lettuce and spinach most of the winter. You can go look the plants in the morning in the winter, and they look wilty, but it's just from the cold. They perk back up once the sun warms up the house.
Because I covered the grass between the beds, it stayed nice and green all winter. It was so pleasant to go into the hoop house, sit on the grass, and pick spinach while it was cold and snowing outside. It smelled like spring all winter long.
For more info about what to grow during the winter check out this book.