For about two weeks 2% of Disqus instances were sending back information about the popular libraries installed on the page. Here is the code we used to check for libraries and their versions:
var jquery = window.jQuery && jQuery().jquery; var jqueryui = window.jQuery && jQuery.ui && jQuery.ui.version; var protojs = window.Prototype && Prototype.Version; var dojo = window.dojo && dojo.version.toString(); var mootools = window.MooTools && MooTools.version; var ext = window.Ext && Ext.version; var yui = window.YUI && YUI.version;
Also keep in mind that the majority of websites that install Disqus are blogs, online magazines and other publications. For example, these stats could be very different among web apps.
(Libraries other than jQuery, MooTools and Prototype had less 0.01%)
We will probably do more surveys in the future about some non-general purpose libraries like Modernizr, etc. Stay tuned.
Thanks to Kim Weisberg for editing drafts of this.