In the next revision to come, there is an important fix, for a problem known as the "terminator artifact". For your information, this artifact is seen at the limit of lighting models that have low-poly subdivision (it is more obvious in low-poly meshes - it actually can be seen on arbitrarily detailed meshes on close up). It is very nicely described in this paper
where it is identified as an inherent render artifact rather than a bug! This is why, you probably have seen this in a lot of other renderers as well.
As far as we know, the majority of unbiased renderers suffers from this problem. In biased renderers, it is somewhat easier to fix the problem. A nice (biased) solution used, is to appropriately tweak the material reflectance, compressing it and "pushing out" the jaggy artifacts. If an inherent solution does not exist on the renderer, the typical workaround is to subdivide models to a finer degree (something that costs both memory and speed).
In Thea Render, we didn't want a solution that could alter/bias material appearance but instead we very carefully compensate for the energy loss due to the terminator artifact dark zones. Our solution produces smooth renders even for very low-poly models with only the basic assumption that the subdivision is uniform (i.e. not abruptly changing). We are actually very happy that we have this working out-of-the-box for all engines. As an example, you can see in the images below some spheres rendered with sun light in current and next (forthcoming) revision (note that the spheres have increasing subdivision detail from left to right).
File comment: Current revision showing terminator shading artifacts.
terminator_artifact.png [ 71.55 KiB | Viewed 3915 times ]
File comment: New (forthcoming) revision produces perfect/smooth shading, artifact-free.
terminator_artifact_treatment.png [ 70.15 KiB | Viewed 3915 times ]
With this enhancement, Thea moves ahead and we believe as an established world class renderer, quality-wise. We are proud of making Thea better and we hope that you are proud of being a Thea user and getting artifact-free renders - getting ahead of unbiased competition.