I did upgrade most files of my plugindemo site http://korpelainen.net/plugindemo and you can test those not-yet-finished plugins with username 'test' and password 'test' there...
I had some info about using those plugins in http://korpelainen.net/mediawiki and you can download either all the latest files with moodle 1.9.9+ from http://korpelainen.net/plugindemo.zip or just the mathplugin files that can be unzipped over existing package (of moodle 1.9.X) from http://korpelainen.net/mathplugins.zip
Once you have unzipped the files (and installed moodle) you need to enable first jsxgraph filter from Administration > Modules > Filters > Manage filters and if you want to test those other plugins you can select them from the same place and settings of math filter. Math filter can be disabled - I used it mainly for getting new settings to moodle 1.9.x - in moodle 2.0 there will be different settings.php files for this purpose.
Next you need to change theme to Math from Administration > Appearance > Themes > Theme Selector to get TinyMCE (Theme base integration) and those editor plugins. I did add script tags to standard theme meta.php and styles of jsxgraphs to standard theme styles_layout.css but usually it's not necessary if you use custom theme like "Math" with extra settings.
Note that these plugins and filters are not bug free or finished for production sites.
It may have some influence to missing mouseover events in calender or some quizzes - I have not tested those places where overlib.js is used in moodle.
Firefox and Chrome have no major problems. Opera and Safari have problems with showing applets (Dragmath or Geonext) in popups of tinymce.
Note that it is always possible to save / export graphs from Geonext applet as gxt code, applets, html, svg or png images so even if the current code is buggy in IE you can use the applets for creating graphs and use other formats for showing the graphs in moodle...
Try for example the attached applet (as an administrator you can add script or applet tags directly to HTMLArea - tinymce may not allow or show them in editor without some changes to init code of tinymce). If you change (user/course/session) themes you can also change editor if needed...