Actually, that normally happens when you visit a the IP address of a machine that is used for the shared hosting plans. Normally, the browser tells the machine its connecting to the "Host" it wants, ie "dreamhost.com"; the machine then looks up its virutal hosts and handles the requests for that domain as necessary. However when you visit by IP address, the browser doesn't send a domain name for a "Host" value, and so the machine can't match to a virtual host.
So intentionally visting by IP address will always result in this message.
If the domain was just added, but the dreamhost servers not finished initializing the web service, this message may appear if visiting by domain name.
Also this message may appear if the DNS is still matching hostname to IP address but machine at IP address is no longer handling web service for that domain; DNS may have been cached or just not updated yet.
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