I personally havn't validated them, I wouldn't really know what validation type to use. I used the xhtml validation once but it gave 'problems' with the closer for the </head> and the </body> and stuff like that...
I'm not the starter of this topic, I'm using the normal versio of IE8. Yet I get all the problems they had n IE6 and I don't understand why. Anyhow, it's better like this, at least I can 'test' it for IE6. I've still got many problems with the site-layout that work perfect in Chrome, Safari, FF, Opera, but not in IE8.