One day, after starting Eclipse 3.2, I noticed astonished that the autocomplete feature for Java classes did not work anymore. On pressing Ctrl+Space the popup list did appear, but it was always empty. This was a time of great mourning, since autocomplete is one of the killer features of Eclipse.
So what was the problem? In the evening of the previous day I did some reorganizing on my computer and moved the Eclipse workspaces to another drive (my operating system being Windows XP). It seems that this alone made Eclipse to fail the autocompletion.
QUICK FIX: Create a new workspace on the new desired location and import the projects from the old workspace. Do not forget to check the “Copy projects into workspace” checkbox so that the projects get copied to the new workspace directory. From this point on autocomplete should be back on its feet.