Depends! Who's your ISP? I'm sure that there are some DNS servers out there owned/operated by companies or organizations that don't mind if you use their DNS services. Me personally, if I owned and operated ISP infrastructure, such as DNS servers, I would want to limit their use to my customers. I'm sure that there will be arguments that DNS is an open system for anyone's use and I disagree with that assumption.
You can go to »
dfw.speakeasy.net and try their DNS servers, they list them somewhere on their site. I have used them and found them to be no better or worse than those of my ISP.