Over at the Google Webmaster Central blog, they’ve announced “Page Speed Online,” which allows users to check out the performance of any page on the internet, at any time.  Users will receive a page performance score calculated out of 100 and will be given prioritized suggestions upon which to improve.

When you run a test for a particular page, you will receive a score.

That score will be accompanied on the left hand side by suggestions for improving the page.
Google ranks these suggestions either high, medium or low priority.  The high priority suggestions are the ones that will give you the most improvement for the most minimal effort.  The medium priority suggestion will not give you as much improvement and may require much more work.  The low priority suggestions are to be concerned with only when you take care of the higher priority ones.

As you can see above, on the bottom right of where you see the number score, there is an option for a mobile analysis.  Google has added support for mobile pages to this new tool:

Due to the relatively limited CPU capabilities of mobile devices, the high round-trip times of mobile networks, and rapid growth of mobile usage, understanding and optimizing for mobile performance is even more critical than for the desktop.

The mobile recommendations are tuned for the unique characteristics of mobile devices, and contain several best practices that go beyond the recommendations for desktop browsers, in order to create a faster mobile experience. New mobile-targeted best practices include eliminating uncacheable landing page redirects and reducing the amount of JavaScript parsed during the page load, two common issues that slow down mobile pages today.

Google also notes that Page Speed Online is powered in the same way as many Chrome and Firefox extensions as well as webpagetest.org.