Give it a bash, if you haven't already; it's great! Basically, it highlights whichever element your cursor is on. This element is highlighted throughout the Java editor, both in the edit area and in the right-hand margin where errors and warnings are shown. (What is that called, by the way?)
And there's more. Put your cursor over a method's return type, and it'll highlight all the method's exit points. Put it over an exception in a method's
throws clause, and it'll show you all the places in your method where that exception can be thrown.