When Force.com released the Visualforce charting feature, they announced a few known limitations and considerations for Visuaforce charting, which are as follows:
Visualforce charting can be rendered only in Scalable Vector Graphics (SVG) supported browsers.
Visualforce charts cannot be displayed in pages rendered as PDFs because Visualforce charting uses JavaScript to draw the charts.
Visualforce charting is not used in e-mail messages or e-mail templates because e-mail clients do not support JavaScript's execution in e-mail messages.
When we develop a Visulforce page with Visualforce charting, we need to use a JavaScript debugging tool such as Firebug to track errors and messages returning from Visualforce charting to the JavaScript console.
Dynamic Visualforce charting (Apex-generated) is still (as of Spring 2013) not supported by the Force.com platform. However, this feature is supposed to be released soon.