Sorry, don't know about OSX (though I'm thinking about getting a Mac
mini to try it out ;)) but one thing to ponder if you go for an OpenGL
backend might be to allow animation in setting up / drawing the
graphs. For example, in a bar graph, first the grid and x and y axes
and labels and then the bars grow up/down from the axis. Just a
thought for a version 2.0 or so... :)

Best,

Robert