One of the more common topics that occurs in the Ajax/DOM/JS space is page load times. This is especially important to the jQuery team and one of the reasons we go to great lengths to keep the library at about 20k total size.
Which leads to Pingdom. If you're interested in seeing how your page is performing, then you might want to take a look at Pingdom Tools. It gives you a great visual representation of how your fast your page loads and the overall size of your page and its components. WebAppers.com has a nice writeup here:
Direct link here:
The only drawback is that you can't use Pingdom for intranet testing. If anyone knows of a good application (other than FireBug) or method of testing page load times in an intranet environment, I'd love to hear about it.
FireBug does have similar functionality but this is a nice alternative to cross-reference with.