The first Internet Explorer 8 Beta has been released at MIX08.The version is primarily for use by web developers who want to test their web sites. A test version for consumers is slated for later this year. The release date has not been announced.
A new feature, called WebSlices, lets users subscribe to specific content on the web page, such as updates about friends on a social networking site. It monitors changes in a pane that drops down from the browser's toolbar. Another feature, called Activities, lets users highlight words on a web page and click them in another online service, such as searching for an address in a mapping site.
Some sites will not work with the new features. There will be an option to set IE 8 to render pages as if it were IE 7.
You can learn more at the Internet Explorer MSDN page, where you'll find a panel all about Internet Explorer 8. A readiness toolkit for IE8 is available to help you get start developing. Internet Explorer 8 Beta 1 is available for download. A summary of features is also available.