@Robert Harrison
MD5 has been broken, now that people can create bogus HTTPS certificates which validate using MD5. So web browsers recently had to be updated to not accept MD5 signatures as valid, rendering invalid MD5 based certificates not by then updated. SHA is a family of hash algorithms, http://en.wikipedia.org/wiki/SHA currently going up to SHA512, likely one of the strongest currently known in widespread use. Some earlier SHA versions are now thought to have weaknesses, though probably not yet as readily exploitable as MD5 now is.
What having a signed DNSSEC root creating a heirarchical global PKI for the first time will mean is that much more attention will be given to the strength of the algorithms used, resulting incorrespondingly more fame and fortune for whoever publishes successful attacks.
We will never know that a particular algorithm is secure, we only know when published insecurities exist. What can be said about their security, for algorithms developed within the public domain, is what it would be worth to the person who succeeds in breaking it and publishing a feasible attack, from which we can estimate the amount of talented effort directed towards doing so without published success. (For the paranoid, we don't known what the NSA and GCHQ knows about unpublished weaknesses, but we can still assume their budgets for maintaining the loyalty of those who do know to keep this knowledge secret is finite. We can also assume they can only use their top secret knowledge for attacks of high enough value to them that these justify the risks of leaking this knowledge in the process of using it. )
In the past attracting this kind of effort has required large prizes on offer to the first successful published attack. But we will need be in no doubt about the fame and fortune that will come to a cryptanalyst who can publish a paper which describes a feasible attack breaking the algorithms used to sign the DNSSEC root.