Making websites mobile-friendly
The blog explains the how the current mix of mobile phones can access the Internet, between traditional mobile phones (i.e. phones with browsers that cannot render normal desktop webpages) and the newer trend of 'Smartphones' (which are phones with browsers that render normal desktop pages, at least to some extent, such as Blackberry devices, iPhones and Android phones).
Google uses 2 types of search engine 'crawler' that are relevant to mobiles: Googlebot and Googlebot-Mobile. Googlebot crawls desktop-browser type of webpages and content embedded in them and Googlebot-Mobile crawls mobile content. The blog post explains how to recognise and serve appropriate content to the Googlebot-Mobile.
Google says they expect smartphones to handle desktop experience content, so there is no real need for mobile-specific effort from webmasters. However, for many websites it may still make sense for the content to be formatted differently for smartphones, and the decision to do so should be based on how website owners can best serve their users.
Most websites currently have only one version of their content, namely in HTML that is designed for desktop web browsers. This means all browsers access the content from the same URL. These websites may not be serving traditional mobile phone users and the quality experienced by their smartphone users depends on the mobile browser they are using and it could be as good as browsing from the desktop.