I'd recommend against completely AJAXing your site, it's one of the biggest mistake new web designers do when they try making their site all "web 2.0." Having your website completely navigated by AJAX breaks the capability for a visitor to use their back/forward button, which is a big no-no. AJAX is amazing, and can be used tremendously well in certain situations, but shouldn't be abused (as it looks like this plugin does).
On a similar note, I personally use
WP AJAX Edit Comments, which serves just one simple purpose, but it does it well, and it has come in useful at times, =)
~Salad