I just had an interesting Twitter conversation with my good friend Oliver Gierke about the new Eclipse 4.2 look.
Oliver did not like the new look and after changing the theme to Classic still complained about the new look. Please note that changing the theme back to “Classic” may require a restart of Eclipse. Please see Bug Report: Theme switching should warn the user that a restart is required for a potential future solution.
So if you do not like the new look, select Window -> Preferences -> General -> Appearance and select “Classic” as the theme. And restart afterwards. Afterwards Eclipse should very similar to what you are used to.