Have you seen any websites ranking well in google without a domain name? I just found one.. Wikileaks. Instead of having a normal domain, they use an IP address in order to rank in Google.
The important thing to rank well in google is a lot of backlinks, preferable from various c-class domains or IPs. If you have this is mind, nothing can stop you.
Update (17 jan): Wikileaks are now using a domain instead of an IP address to achieve good rankings in search engines.