Consistent with our efforts to promote further interoperability across the Web, Microsoft will be releasing Internet Explorer 8 to render content in its most standards-compliant way by default. Giving top priority to Web standards interoperability allows us to help web developers and designers drive toward the ideal of "write once, run anywhere", freeing up more time to innovate rather than modify content for different browsers. This commitment also addresses several development and design pain points from previous Internet Explorer releases.
However, browsing with this default setting may cause content written for previous versions of Internet Explorer to display differently than intended. This creates a call to action for site owners to ensure their content will continue to display seamlessly in Internet Explorer 8. As such, we have provided a meta-tag usable on a per-page or per-site level to maintain backwards compatibility with Internet Explorer 7. Adding this tag instructs Internet Explorer 8 to render content like it did in Internet Explorer 7, without requiring any additional changes.
We are encouraging site administrators to get their sites ready now for broad adoption of Internet Explorer 8, as there will be a beta release in the third quarter of this year targeted for all consumers. To learn more and get started, please follow the step-by-step instructions located at KB952030
Link: MSDN Blogs.