If you've installed Pydev with the zip files, you are probably having problems with code-completion. This happened because in the process of updating pydev to P2 (which is the new way of installing eclipse plugins), the zip files ended up having the update site and not the plugins in the format they should be installed.
You can fix that by uninstalling pydev and then instead of making any extract, go to help > software updates > available software > add site > archive and add each zip file there (org.python.pydev.feature-22.214.171.12436.zip and com.python.pydev.extensions-126.96.36.19936.zip), which should use those files correctly as an update site.
The error that appears in the error log if that's not done is something like:
Error creating python process - exited before creating sockets -
exitValue = (1)(/usr/bin/python2.4