One thing thorium proponents tend to omit is that there was a German thorium reactor which was considered to be in regular service (i.e., non-experimental). It suffered an incident and was shutdown several years thereafter as the costs of dealing with the incident and ensuring safety overwhelmed the operating company and forced it to seek a government bailout.
So there is some negative experience with Thorium. And the Germans are not willing to try again. Since the Germans that designed that reactor have the most experience with Thorium, and they are not trying again this should give a bit of a pause for others.
However, China is licensing those German designs and will try similar reactors in the coming years so we will see how that goes.
It can not be stress enough that the reactor must be a molten salt reactor. The molten salt provides the stability, safety, and efficiency gains that a normal light water reactor can NOT match.
So there is some negative experience with Thorium. And the Germans are not willing to try again. Since the Germans that designed that reactor have the most experience with Thorium, and they are not trying again this should give a bit of a pause for others.
However, China is licensing those German designs and will try similar reactors in the coming years so we will see how that goes.
See :
http://en.wikipedia.org/wiki/THTR-300
http://en.wikipedia.org/wiki/Pebble_bed_reactor#Thorium_High...