Google detail browser support planon Jun 02, 2011 in HTML5 by Martin Tyler
I’m sure this has been mentioned before, but maybe this is more specific details, but Google have decided to only support the latest two versions of any browser. As soon as a new version is released, an older one will stop being supported.
That means no more support for IE7, FF3.5 or Safari 3.
As they mention, things won’t just stop working for those browsers, but they won’t be officially supported.