Related link: http://dnsmon.ripe.net/
The RIPE Network Coordination Centre (RIPE NCC), one of four Regional Internet Registries in the world, has recently launched a beta version of dnsmon.
dnsmon provides a comprehensive, objective and up-to-date overview on the quality of service of high level DNS servers, currently these are the root servers and some participating TLD servers. dnsmon measurement data is continuously added once every hour.
Please note that the dnsmon service is still beta.