This is a small part of a very large list :
As of 8/1/2011, Google has announced that it would be dropping support for older browsers such as Mozilla's Firefox 3.5, Internet Explorer 7 and Apple's Safari 3. In 2010, it ceased supporting Internet Explorer 6, Firefox 2.0, Safari 2.0 and their own Chrome 3.0.
Citing the need for advanced browsers to handle its new HTML5 features such as Gmail Desktop Notifications and Google Docs drag and drop file uploads, Google said it will only support the current and the previous major releases of all popular browsers i.e. Chrome, Firefox, Internet Explorer and Safari on a rolling basis beginning next month.
That is, each time a new version is released, Google will begin supporting the new update and drop support for the 3rd oldest version.
As for users who are still on older browsers, Google warned users stating that all its services i.e. Gmail, Google Calendar, Google Talk, Google Docs and Google Sites will eventually stop working completely on these browsers.
Here are some of the other major web sites and organizations that have, or will, officially stop supporting (will make no guarantees their sites and products will work with) Internet Explorer 6: