I lose my mojo for weeks at a time, but usually keep reading the QB and eventually something comes up that I just have to try. Sometimes the reason for a slump is that I've reached a part of the quilt that I haven't decided about or just don't like to do, or I don't like the top I made and don't feel like spending more time on it. Our guild does a lot of charity work, and there is always someone who is happy to complete a quilt that someone else burned out on. If I hate it for no good reason, I donate it. Then it's a lot easier to get into the next one. The work and the materials are not wasted. They just went to a different purpose than I had in mind when I started, and I can feel good about the contribution.
Oddly, I may turn around and finish a charity quilt that someone else pieced, and that always seems to give me a little boost in my enthusiasm. We don't have deadlines for the charity work, but I have internal deadlines - I want to get that done by the next guild meeting, so it's almost always something I don't put off. Then I often find myself back in the quilting habit.
If we could buy motivation in a bottle it would be the hottest item at the store.