I use Mootools and FusionCharts the same time. When I include FusionCharts.js after including Mootools.js, the JSON object in Mootools seems be overwriten by JSON defined in FusionCharts. Otherwise, when I include FusionCharts.js before including Mootools.js, the JSON object is properly handled (mootools append attributes to the JSON object, not overwrite the JSON object).
I test this and find that only IE7 has this behavior.
code in FusionCharts:
var JSON;JSON||(JSON={});
code in Mootools:
if (!this.JSON) this.JSON = {};