So I've been poking around with IE 8 now for months during the beta and rc process and been noting some changes out in how IE8 on a deeper level for some of my applications.  There are a few worth noting:

• ASP.NET
  • So Microsoft has broken some items in the .NET framework and AJAX through the IE process.  The first and most notable thing that is broken is the ASP.NET menu system.  If you use IE8 with a menu you will notice that the menu will appear as a white box instead of the normal box.  This is due to some changes in CSS and the zIndex not working correctly.  You can this by checking out this post:
    
    http://blogs.msdn.com/giorgio/archive/2009/02/01/asp-net-menu-and-ie8-rendering-white-issue.aspx
• Concurrent Open Windows
  • This has been a tough cookie to crack in IE 6/7 with windows opening pop-up windows with update/panels.  The two current download/concurrent processes in IE 6/7 causes your browser to hang while the process in the background closes.  In IE8 that has changed from 2 to 6 so the problem still exists just not as badly.

More to come as I find more of the problems.