If you are finding Eclipse is getting slower the most likely cause of this is leaving projects open. When projects are left open the incremental compiler will compile "Open Projects" in the background at start-up and save.

To close a project go to:

"Navigator" panel, Right-click on the Project Folder and "Close Project"

Alternatively, from Eclipse 3.2 onwards you can

Right-click a project and select 'Close Unrelated Projects'