In the post it says they instrument the $.get callback, but that's a jQuery function. So are they instrumenting actual AJAX methods or just jQuery's? Can you get timing data for JSONP requests, which don't actually use AJAX (but jQuery hides that for you)?
If you're interested in an OS alternative, Bucky also times AJAX requests: <a href="http://github.hubspot.com/bucky/" rel="nofollow">http://github.hubspot.com/bucky/</a>
Just noticed my cool little Browser(beta) menu today!<p>Cool stuff, especially given that it's being offered for cheap Lite users like myself. I was happy with average req times; this is just icing on the cake!