IE8 has been released several weeks ago at the MIX Web conference. Next week the actual rollout via Windows Update will start.
You can watch the MIX keynote speeches online and there is also a nice video showing that JavaScript performance is not everything.
I have tested IE8 RTM the past few weeks and can really recommend upgrading. IE8 is faster and more secure than IE7 and has cool features such as tab coloring, standards-compliant CSS 2.1 support and a great built-in script debugger.
If you have not done already, please also update Quero to the newest version, which I optimized for IE8.