Since the Workspace Mechanic for Eclipse has been migrated to Git, the update site URLs have changed.
The main repository can be found at http://workspacemechanic.eclipselabs.org.codespot.com/git.update/mechanic.
The testing repository can be found at http://workspacemechanic.eclipselabs.org.codespot.com/git.update/mechanic-testing.
The old repositories will be left for a period of time, but eventually removed. Please feel free to follow-up with questions on the mailing list.