Drawbacks: Highcharts, like Google Maps, does have a distinctive look, so you may want to customize the Highcharts stylesheets so your visualizations don't look like numerous other Highcharts on the Web. While charts displayed fine for me on an Android phone, they weren't interactive (they were on an iPad).
Skill level: Intermediate to Expert.
Runs on: Web browsers
What it does: How often do you have data in one format -- while your application needs it in another? New York Times interactive graphics editor Shan Carter ran into this situation often enough that he coded a tool that converts comma- or tab-delimited data into nine different formats. It's available as either a service on the Web or an open source tool.