I find it hard sometimes to continue my development momentum when my applications user interface is not developed nicely. On the other hand, if I have a UI then has all the elements of the application, I find that I am much more excited about the project. I think the main motivation is that I have a clear picture of where I'm headed, and I already have the end goal in plain view. Having the end result infront of me allows me to reverse engineer how I want to go about designing the application also....