//http://www.avajava.com/tutorials/lessons/what-is-a-working-set-and-how-do-i-use-it.html
Working sets are a great way of filtering sets of projects in the Navigator view. They are particularly handy when you have sets of projects that go together. For instance you might have a 'domain' project and a 'view' project and a 'utility' project and a 'build' project that all go together for one work assignment, yet you might have another assignment that consists of three other interrelated projects. You could create a Working Set for each of these assignments and switch between the sets using the Working Set pulldown menu available by clicking on the white downward arrow.