You may have heard that IE8 will suppress subdomains on sites. This means if you have a website with a subdomain for different channels/sections - e.g. videos.cnet.co.uk it will display as cnet.co.uk in the address bar - i.e. no subdomain.
Why would they do this? I suspect they are doing this to assist dim wits that get caught out by phishing scams. They get sent a mail saying they have to update their account details or some other random reason for them to login to their bank or paypal online account. They are then given a link to the attackers website and although it looks similar to the site they expect to see it is all fake and a way of getting hold of their login details. To help trick people many register domains like "uklogin.com" and then use subdomain "natwest" or "paypal" so the url looks like http://paypal.uklogin.com and the naive user assumes they are on the official site. By hiding the subdomain Microsoft it seems are making it more obvious to users what the true domain for the site they are using is.
Why are they ruining the subdomain to help the dim wits? They already have phishing filters and this fix will affect legitimate sites not just scammers.
I hope this is one of the features that doesn't make it past beta.