In 2009, site speed became a ranking factor and Google launched several tools for webmasters to track their site speed. One of those tools was launched in December 2009 and it was found within Google Webmaster Tools under the name site performance.
The tool has had its issues but those issues are popping up again. It is just about 30 days out of date now.
A Google Webmaster Help thread has complaints that the tool has not been updates for a while.
I checked several accounts and the latest data I have for that report is February 20th! Here is a screen shot:
As you can see, that was a while ago.
Googler, Pierre Far said:
Thanks for the reports everyone. I've passed it on to the relevant team internally.
Forum discussion at Google Webmaster Help.