On Retina displays the jqPlot graphs look really blurry. There's a relatively simple fix for jqPlot available that hasn't made it into the upstream repo: http://stackoverflow.com/questions/20221461/hidpi-retina-plot-drawing/20228300#20228300
Since Piwik makes heavy use of jqPlot we should fix this ourself and maintain the fix until it is merged into the jqPlot upstream repo.
In 9c58e9d: This modifies jqPlot to support retina displays.
This modifies jqPlot to support retina displays.