To keep himself inspired and working on his first novel, Kerouac developed this convoluted system to equate how much he wrote each day to a baseball batting average. His "formula" has something to do with how much of his daily goal he completed. A good day of 3000 words would give him a batting average of .380. The less the number of words written, obviously, the lower the average. Most days he hovered around .320, or 2000+ words.
About the only thing that works for me is setting deadlines for myself; I often get the most done when I find a mag or contest is closing to submissions in a couple of weeks. But I'm wondering what other methods people have developed to keep themselves motivated. It's probably my big weak spot, so I'm always curious how others keep themselves going when the work drags and real life interests persist in interfering.