Yes, it is definitely worth going over OpenGL tutorials! ES is basically a subset of OpenGL v1.something_or_another. With the exception of a few small differences, you can run the same OpenGL ES code on the Mac as the iPhone. So it might be worth you hunting down some GLUT demos that you can run on the Mac. Even if they use immediate mode rendering, ie code that uses glBegin() ... glEnd(), there will still be a lot of code that is relevant for ES, eg transformations, blend modes, fog, vertex arrays and so on.
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