Robert, if you read these two threads you'll see that I use Artlantis because it offers superior workflow and output to Renderworks:
http://techboard.nemetschek.net/ubbthreads/showflat.php?Cat=0&Board=UBB20&Number=60663
http://techboard.nemetschek.net/ubbthreads/showflat.php?Cat=0&Board=UBB20&Number=60356
In fact there are some screenshots of a project that I simply could not have completed if I had attempted to do them with Renderworks. The difference is that big.
I'd rather see Renderworks compete on merit but, frankly, if it's going to be a obstacle to better interoperability with 3rd party rendering tools (as per my link above), I'd rather NNA dropped Renderworks altogether. In fact this is not such a silly idea either, as it seems that the main obstacle to Renderworks working on a level to that of Artlantis is that fact that it's tied into the Vectorworks environment.
Update: URL corrected