Site Performance, an experimental feature added to the Webmaster Tools console courtesy of Google Labs, provides detailed information about your site’s load time and gives suggestions for speeding it up. It includes a chart of your site performance data over time, which can help determine latency triggers.
As explained in Google’s official blog post about it, the Site Performance console includes examples of specific pages and their actual page load times, plus Page Speed suggestions that can help reduce latency.
I was pretty shocked when I logged into Webmaster Tools today to find my blog pages take an average of 6 seconds to load. Google states that this is slower than 83% of sites! The Example Pages and Page Speed Suggestions revealed the culprit was a banner ad that was not optimized and a couple of extra DNA fetches on some pages so I was able to fix the issues pretty quickly.
The load time data is apparently sourced from aggregated information by users of the Google Toolbar but it’s important to remember that it’s all averaged. A specific user may experience your site faster or slower than the average depending on their location and network conditions.
As a Labs tool, Site Performance is still under development and Google are seeking feedback on it via the Webmaster Tools Forum.