I know your feeling way too well! I am the kind of person who invest himself in what he is doing until I am tired and I switch back to an old project. I move from one to the other each time I am bored, would that be java programming, making movie in final cut express, drawing, maya, etc...

The solution I have found to prevent this 'problem' is to never do too much. For exemple, if I am working on a model and its about 11hPM, I have the choice of either going to sleep or to keep working on it for an hour. As much as my mind wants me to keep working on it, I dont. This need a lot of willpower (especialy if the adiction is a game!) but its the best way to never get burned because you always keep your interest.

Also, you can show your work to others to get some cheers and motivation. Nothing better than the interest of others to boost yours in your project!

Good luck!