I've seen it tossed around that having ns the same as your domain name is a possible sign of nefarious intententions. And I'm sure it's true in some instances.
However, one of my hosts specifically asked me to purchase a domain to be used as my name servers. I don't use that domain for anything other than ns...but a whois lookup on that domain does in fact reflect my company information...not that of my host.
Doesn't really answer your question fully. But, just a heads up that there are legit webmasters using custom ns instead of those of their host
