Yes, I should have been emphatic that part of the problem with not understanding DNS is that if you don't understand it, you might not even realize that your problem is DNS-related.
Whenever I hear, "X is slow!", my first response tends to be, "Are you sure it's not DNS instead of X?" About 50% of the time, DNS misconfiguration is at least a component of the problem if not the entirety of it.
DNS touches every service on the Internet. If you get it wrong, you break every service, sometimes in subtle ways.
tools like dnstracer (http://www.mavetju.org/unix/dnstracer.php) and dig are very useful for diagnosing these issues, but you really need to understand the fundamentals of how dns and delegation work.