The compatibility table on QuirksMode have been updated with information on IE8 in both standards mode and Compatibility View mode.

CSS contents and browser compatibility

Today, many Web sites provide content updates through Really Simple Syndication (RSS) news feeds. This requires a Web site to duplicate some content as a special XML file, called a feed, that a news reader application can download and check for updates. In contrast, a Web Slice enables users to subscribe to content directly within a Web page; a separate feed file is not required. Users monitor content changes and view the updated portion of the Web page directly from the Favorites bar (the improved Links toolbar) of Internet Explorer.

http://msdn.microsoft.com/en-us/library/cc196992.aspx

Reports of broken sites are an important part of the feedback the IE team receives from the community. When they receive a report of a broken site, they take it and identify the core issue causing the problem. A number of these issues end up being side effects of changes they deliberately made in IE8, but even these are useful. They help the team identify which IE8 changes have the broadest compatibility impact. In this post they share some of these issues with us so we can quickly identify problems affecting our sites when migrating from IE7 to IE8.

http://blogs.msdn.com/ie/archive/2009/03/12/site-compatibility-and-ie8.aspx