How to sustain enthusiasm in grad school?

The answer is - work on multiple projects and collaborate with multiple and diverse people. Some of my current projects are:

1. Collaboration with 500-bed teaching hospital to collect disseration data on role of information and communication technologies in alleviating emergency department overcrowding.
2. Collaboration with the above hospital to understand patient flows and evaluate a new resource-based patient flow in their emergency department
3. Collaboration with faculty and graduate students in the Industrial Engineering department to simulate patient flows in the emergency department of above hospital.
4. Collaboration with the Intelligent Agent Laboratory to examine if agent-based architectures can be deployed on mobile platforms to help collaboration among pre-hospital and emergency department staff during mass casualty incidents.
5. Collaboration with faculty and grad students at the College of Education to understand how culture affects technology-career adoption among women in high school. (This project will involve collaboration with a high school in India).

I am one of those people who love to do multiple diverse things at the same time and I wish the above list were longer, but its been pretty hectic working on the these five projects. Project 5 is not related to my research interests but is the one that I am having the most fun with.