The Site Speed area can only been seen using the new Google Analytics (GA), and only if you turn it on. You'll find it located under the Content heading.
By default, the GA code does not include page speed tracking. The first step you will want to take to enabling this, is go into your HTML code and add the line that tracks it.
For the not-so-squeamish, this can be done easily by adding the _trackPageLoadTime() function to the list of functions you give Google Analytics. Quite simply, find the line that reads:
and add this line immediately below it:
If you have no clue what that means or need additional help, Google provides a complete article explaining the code in the Analytics Help Center.
Google's function measure uses the same NavigationTiming specifications published by World Wide Web Consortium (W3C). It measures starting from the user click until complete loading of all elements on a page. While this standard requires newer versions of browsers, Google has set some fall back support into place. It will also accept data from the Google Toolbar, if installed on older browsers without support for NavigationTiming.
The Site Speed Report will let you know which pages on your site load slower than others. When combined with advanced segments, it can also help you determine if certain geographic regions or other types of users -- based on connection speed or browser type, for example -- have slower page load times than others.
As with any metric in Google, your mileage may vary. None of the metrics, including site speed are guaranteed to acquire data for 100 percent of your visitors. However, it will give you a basic representation, based on its sampling. Use it well for trends and patterns, but not for overall hard numbers.