Something I think gets lost a lot in data visualization is that the goal is not to make things look pretty, it is to convey lots of information quickly and clearly. If it looks pretty as well, great; but don't lose sight of the clear presentation of information. There are things the human perceptual system doesn't do very well, such a judge/compare angles and areas. Line lengths and coordinate look up work much better. So be wary of bubble and pie charts, and stick to line graphs and scatter plots.