Google Chrome 6 allows using "Web Timing" located under window.webkitPerformance, that let web developers measure true page load time by including 'time to request, generate, and receive HTML document'. "timeline below illustrates metrics it provides. vertical line labeled "Legacy navigation started" is the earliest time a web page can reliably measure without Web Timing. In this case, instead of misleading 80ms load time, it's now possible to see that user actually experienced a 274ms time. Including this missing phase will make your measurements appear to increase. It's not because pages are getting slower – we're just getting a better view on where time is actually being spent," explains Google.
Web Timing metrics are under window.msPerformance in 3rd-platform preview of IE9 and work is underway to add window.mozPerformance to Firefox.