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Whois.sc
Well first of all, generally when people say 'web hacking,' they refer to software hacking run as a website itself, not the server behind it. Overall, it is good to accumulate information about a target, but a whois wouldn't help you very much.
Also, realize that there are many databases of whois information, all containing nearly identical information. Don't think that one site is all that's out there.
Just for a little background, whois.arin.net is one of the better known databases. Whois information was never meant for being run for websites initially, it was meant for shell-only interfaces, using the unix application WHOIS. It is just a generic networking tool.