I've got a site that I developed targeting mainly IE 8 (and IE 7 to some degree), but not IE6. I spent development testing in a Windows XP VM with IE8, but now that development is very far along I've noticed that it looks about like IE6 would render it when viewed with IE8 on Vista. I thought it was because on Vista, IE8 may default to IE6 mode, so I set up my webserver to send this header, verified by Firebug:
X-UA-Compatible: IE=8
But that doesn't seem to have worked. Am I missing something here? Is IE8 really that different on XP vs Vista?