<p>I'm about to start testing an intranet web application. Specifically, I've to determine the application's performance.</p>

<p>Please could someone suggest formal/informal standards for how I can judge the application's performance.</p>

To test the front-end then YSlow is great for getting statistics for how long your pages take to load from a user perspective. It breaks down into stats for each specfic HTTP request, the time it took, etc. Get it at
http://developer.yahoo.com/yslow/
Firebug, of course, also is essential. You can profile your JS explicitly or in real time by hitting the profile button. Making optimisations where necessary and seeing how long all your functions take to run. This changed the way I measure the performance of my JS code.
http://getfirebug.com/js.html