A Google Webmaster Help thread has reports of page load time speeds spiking up to ridiculous numbers in the new Google site performance reports. Google's response to these reports was pretty interesting, I'll get to that soon, firs the context.
A Top Contributor in the forum wrote:
After about 6 months of "flat line" Site Performance reports of averagepage load time around 1 or 2 seconds, I am now seeing in Tools a report that: "On average, pages in your site take 83.1 seconds to load (updated on Dec 7, 2009)." and of course the graph has shot up and I'm tol that my site's average page load time is "slower than 100% of sites".
However, the only two pages listed in that report both show load times of 1 to 2 seconds.
Now a Googler with the code name "sreeram" replied saying:
The 83s number is bogus. Your site's toolbar traffic dropped by more than an order of magnitude in the last few days. You should ignore the average for now. We'll soon be showing site owners some indication of how trustworthy the numbers are, so you can decide when to ignore it and when not to.
Not all URLs may have toolbar traffic, so it's possible to have many URLs indexed, and even visited by users, but only a couple may show up on Site Performance. In addition, when there's very little data for a given URL, we won't display it (for privacy reasons), though it will be included in the overall site average.
So in this case, the site's traffic as seen by the Google Toolbar dropped significantly, which caused a weird spike in the webmaster's site performance reports. Thus, Google promised to provide an "indication of how trustworthy the numbers are" in this report.
Clearly, some of these numbers are not trustworthy, such as factoring in Toolbar fluctuations or Google Analytics speed.
Forum discussion at Google Webmaster Help.
Update: John Mueller from Google sent me a note about this:
The Webmaster Tools team is constantly working on ways to improve the product as well as the data provided there. In general, we prefer not to comment on possible future releases. The Labs section in Webmaster Tools allows us to easily try out and iterate on new and innovative features, which is one reason we launched the Site Performance tool there. Personally, I found the data provided there quite actionable and have seen a lot of positive feedback from webmasters around this tool. To fine-tune a website with regards to speed, it can be useful to start with the information provided here and then to look into the details using browser-based tools such as Page Speed and Speed Tracer.
We're always looking into ways we can take our products and services to the next level. We appreciate all of the feedback and coverage that you provide! I'll get in touch with you once I have more information that I can share.