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If I have a simple 2D scene and I want to move the objects inside the scene on the X and Y axis, should I send OpenGL the original vertex coordinates with each move and apply a ModelView matrix transform, or should I simply send the updated coordinates?

Since the scene is simple and there are really not that many vertices, I'm not using vertex buffers.

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The proper way to do it is to use the ModelView matrix to move your object. The object's vertices are defined in the local space of the object, and it's generally good practice not to disturb the data.

This scales well to complex 3D objects and animation because the joint transforms and ModelView matrix operations can be done much faster in a shader than in software. Even if your scene is simple, it's good to adhere to the proper methods.

UPDATE: It's still ok to modify the ModelView matrix outside of the shader. For each object, this only means that we'll do 2 or 3 matrix-matrix multiplications per-frame outside of a shader, and then N matrix-vector multiplications inside the shader, where N is the number of vertices in the object.

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Makes sense. So the best way to do this would be to calculate the matrix transform inside the shader, and only pass attributes containing the X and Y values to translate? –  rid Apr 9 '12 at 5:05
    
If you really wanted to get all the performance you could out of a shader, you could do that I guess, but it kind of over-complicates things. I've updated my answer to explain why it's still ok to modify the ModelView matrix outside of a shader. –  ktodisco Apr 9 '12 at 5:48

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