The number of nameservers can and does vary. Most hosts have at least two nameservers and others have three or more. I believe RFC recommends three and all being on separate c-classes. Again, it varies upon the host and not all follow that requirement.
-Steven | u2-web, LLC - Clustered Shared Hosting "It is the mark of an educated mind to be able to entertain a thought without accepting it" -Aristotle
I will also have to say that we only use two nameservers as well. The reason some hosts have more than 2 is that have each name server pointing at a different ip on the server box. Which may mean 2 name servers are through one data port and one network, while two more name servers and ips are on the second network port and a different network. That allows them to give a more redundant access to the web server, in case there are network outtages, or even some customers cant connect through one network because of their trace route.
While other use multiple name servers to point at a different things, such as a mail server. Also some hosts who run cluster servers, some name servers might point to another server all together where your site is also located.
Even some hosts just have multiple name servers that point to 4 different ips on the same server box going through the same network and port.
It is all dependent on how the individual hosting company operates.
Yeah its usually two. I had a client who was using netfirms and had problem or issue with nameservers he contacted there support and they were very helpful i suggest you do the same thing. I'm sure they will help you out.