I had the same issue after upgrading Eclipse to Indigo while upgrading Ubuntu.
After installing PDT, all .php source files opened in a text editor (instead of the php editor), which means that no syntax or autocompletion was highlighted (the text was grayed out).
To fix it -
Window β Settings β General β Editor β File Associations
The first text editor was specified in the entry for "* .php".
I deleted the entry for "* .php" and recreated it, phpEditor appears first in the list of editor associations.
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