The Internet Explorer 8 team has committed to interoperability and Web standards. It means that viewing pages in IE8 Standards Mode isn’t opt-in, it’s the way the product works out of the box.
The Internet Explorer 8 team has put together a blog posting, entitled Just The Facts: Recap of Compatibility View. The posting explains what the team has done with Internet Explorer."We want to both respect the site author’s intent AND create a positive end user experience," the posting says.
There's support for CSS 2.1, a better Document Object Model, ARIA, and cross-domain requests (XDR) and cross document messaging (XDM) and a start on HTML5 support. You can add a X-UA-Compatible tag to your page so that it will render as older versions of IE. And Compatibility View lets users continue working with existing Web sites that have not implemented the tag, but have special code for earlier versions of IE.
There are other features that developers can take advantage of with IE-8. And you can add the features to you pages without having to write additonal code for earlier browsers. For example, if you add Web Slices or Accelerators to your page, the pages render the same. It's just that Internet Explorer 8 adds some cool features for your site, differentiating the user experience.
In addition, there's Developer Tools that help you debug and view your pages.