A hobby greenhouse can not sustain a large crop of course, but it can, however, give you a place for a tomato plant or two and some fresh greens even in the northern regions.
Greenhouse growers have an organization, called the Hobby Greenhouse Association, which even publishes a quarterly magazine. This organization sponsors events and helps individuals socialize and collect information for the type of gardening that they have an interest in.
Growing for seeds or even growing hobby cactus is possible. With hobby greenhouses it is possible to have several built together that offer different microclimates for growing a large variety of different plants that otherwise would not be possible in your climate.
For more on this subject please go to my page over at Squidoo.