If you’re on Windows 7, you may know this odd behavior: For some reason, Eclipse goes into a build frenzy. Every few seconds, it will rebuild the workspace.
The reason: You added your workspace to a Windows 7 Library and you have “Refresh Automatically” enabled.
My guess is that indexing of Windows 7 Libraries creates temporary files which make Eclipse believe something changed in the Workspace. Which causes a rebuild. Which makes Windows re-index the workspace.
Workaround: Remove your workspace from the library or disable “Refresh Automatically”.
See also: Bug 342931 – Windows 7 Libraries trigger rebuilds