Chris Wilson from IE talked about the new features.

• Beta1 is all about developer and web authors features, getting the platform ready. A later beta will have user experience improvements
• Predictable Experience for Users:
  • Domain Name is Highlighted in Address bar
  • Improved Manage Add-Ons Experience
  • Improved ActiveX: Per User ActiveX Install without admin, Per Site ActiveX Controls, DEP/NX code execution prevention
  • Users Sites & Applications must continue to work with a new browser
• Improved User Productivity
  • IE 8 is resilient after crashes - the frame continues to run, only the tabs gets reloaded
  • Support unlocking the web with W3C ARIA
  • Improved Zoom capability (Page layout is preserved)
  • Everyone uses lots of web services and it is manual.For this there is Activities now. It is implemented with OpenService. As a service provider you can check for your service being installed, if not prompt for install. (ie8.ebay.com has a sample)
  • Portions of a page is important, that's where Webslices comes. (ie8.ebay.com has a sample). It uses the Windows Feed infrastructure to keep it refreshed.
  • Complete CSS 2.1 Compliance
    • Generated Content and Counters
    • New 'display' values for tables
    • Outlines
    • CSS 3 Box-Sizing Property
    • CSS 3 Vertical Text
    • Unbiased CSS Test suites
• All IE8 CSS/JS have a debugger in the box.
• Most of the performance problems were Network Perf is frequently the problem
  • In Broadband the parallel connection limit increased to Six from two
  • JScript improvements
  • CSS Selector API
• HTML 5.0 Offline storage, offline/online events

Beta 1 is available from here | Complete coverage on IE 8 can be read from IE blog.