version.bind text = "9.2.4rc6"
So, if 'dns.roflcopter.com' actually existed, they are running 9.2.4.rc6.
On any DNS server that I have running BIND, I tend to fake the version returned, so this isn't always accurate. You can accomplish this by setting 'version' within the options section of named.conf
version "Go away"
Why? I don't like users knowing the version numbers of software I am running. Worms and script kiddies love looking in search engines/etc for versions of software that can be easily exploited. For instance if your system advertises that it is using "Whizzbang 1.0.1" and a new exploit comes out for any version of 'Whizzbang' earlier than 1.0.2, you will most likely have people trying to get in. Of course most scripts will just try a brute-force attack, and if you are vulnerable, you are already hosed.