I decided to specifically run the tool on the blog post that announced it and Google scored only 73 out of 100 on the mobile speed side but 99 out of a 100 on the mobile user experience side.
Here is a screen shot:
Here are the new features:
- Configure the viewport: Without a meta-viewport tag, modern mobile browsers will assume your page is not mobile-friendly, and will fall back to a desktop viewport and possibly apply font-boosting, interfering with your intended page layout. Configuring the viewport to width=device-width should be your first step in mobilizing your site.
- Size content to the viewport: Users expect mobile sites to scroll vertically, not horizontally. Once you’ve configured your viewport, make sure your page content fits the width of that viewport, keeping in mind that not all mobile devices are the same width.
- Use legible font sizes: If users have to zoom in just to be able read your article text on their smartphone screen, then your site isn’t mobile-friendly. PageSpeed Insights checks that your site’s text is large enough for most users to read comfortably.
- Size tap targets appropriately: Nothing’s more frustrating than trying to tap a button or link on a phone or tablet touchscreen, and accidentally hitting the wrong one because your finger pad is much bigger than a desktop mouse cursor. Make sure that your mobile site’s touchscreen tap targets are large enough to press easily.
- Avoid plugins: Most smartphones don’t support Flash or other browser plugins, so make sure your mobile site doesn't rely on plugins.
All my sites do need work based on this tool, and so does Google.
Forum discussion at Google+.