Flex Builder Multiple Project Performance Tip
You can close a project in Eclipse which keeps a reference to the project but does not load the project. This keeps the Flex Builder memory usage and build times down a little if you are working in a lot of projects at one time.
From the Flex Builder help docs:
Closing and opening projects
To save memory and improve build time without deleting a project, you can close it. When you close a project, you collapse the project and its resources while keeping a reference to it in the Navigator view. A closed project requires less memory than an open project, and is excluded from builds.
To do this select the Project in the Navigator view, then right click and click on Close Project.
With a current state of 34 projects in my Flex Builder workspace the difference in startup memory usage was about 11Mb all closed to 18Mb all open. Not terrible alot of very bit counts, also this would be much higher if I had kept many files from those projects open in the Editor view. Eclipse loads each project that has a present file in the Editor view when loaded. With two files from two different projects of my 34 projects open when Eclipse is started caused it to start at 40Mb memory usage. Granted you need to use memory when you working on projects, but using the close project feature can help you manage what Projects and resources you are using more easily.