I'm not sure trailers are useful, but making them keeps writers out of trouble and off the streets while they attempt artistic endeavors well beyond their talent and training.
Fortunately, I've got over a month until "Ultimate Duty" hits the e-stores. It will most likely take that long before I can make a semi-decent trailer out of odds, ends, royalty-free music and royalty-free art.
I'm using Windows Movie Maker because it's also free. Come to think of it, I'm really cheap, so everything I'm using has to be free.
You tell me. Have you done book trailers for your own releases? Do it yourself or hire it out? What are your experiences?