Here is a partial transcript of a LiveChat I had with Apple Support - hope it helps.
NJ: I have already left MobileMe for iCloud. Need to know how to transfer the iWeb-created (on my MacBook Pro) website(s) to a new host, assuming that "hosting" will disappear MobileMe.
Apple: I can certainly understand wanting to ensure your website is safe and would be happy to provide you with the information that I have here. iCloud does not have hosting space. You will need to obtain a new website host. For 3rd party options similar to iWeb publishing, I recommend using the search string 'website hosting' in a search engine. It comes up with options such GoDaddy, HostGator, and Yahoo.
I always advise backing up your domain file on your Mac: http://support.apple.com/kb/HT1105 and then you would move the website to the new host using the steps here: http://support.apple.com/kb/HT4686 .
NJ: Will formatting be lost? Will I still use iWeb to edit/create websites? or do I have to re-create everything??
Apple: The website can continue to be published to your new host through iWeb. I apologize but the iWeb Application isn't my area of expertise, but for the best support concerning moving your website from MobileMe to the new host is going to be iApps. They will be able to tell you about any formatting when publishing to your new host. No, you will not need to recreate the whole website.