Over the course of the last few months, my Eclipse has become very slow to open. From what I noticed, it was the FlexBuilder plugin pieces causing the delay. Fortunately, it turned out to be my fault.
The trick to speed up Eclipse? Close the Projects you aren't using! I had over 60 open projects. By selecting the project, Right-Clicking and choosing 'Close Project' this seems to help a lot. You can select and close a bunch of projects at the same time. Very nice indeed when closing 60+ projects.
Of course, select the closed project, right-click and choose 'Open Project' when you wish to work with the contents of the project.
From 1.5 minutes start up to < 20 seconds... I am a happy man.
Also, you can close Open Perspectives by right-clicking on the perspective (in the top right-hand corner) and choosing 'close'. This works well for less commonly used perspectives like SQLExplorer and the like.