With IE8 coming in the not so distant future, Microsoft describes what's new for developers in this Readiness page.

http://www.microsoft.com/windows/products/winfamily/ie/ie8/readiness/DevelopersNew.htm

Google toolbar crashes IE 8 when the user goes to certain web sites. It crashed for me when I visited http://my.ebay.ca  and  http://www.google.com/ig

Way to reproduce:

• Install Google tool bar, in my case toolbar was installed when I upgraded.
• go to http://www.google.com/ig Google toolbar gives you a crashed warning and takes IE with it.

Severity can be high if you had already set http://www.google.com/ig as your home page because you are stuck in an endless loop that can only be fixed if you uninstall the toolbar. Note that the crash doesn't occur if you are in Emulate IE7 mode.