Captain Obvious what do you mean with results aren't great? you are referring to render time or to final result?
I love Corona, but iRay delivered pretty neat results for me until I started to work with Corona, the bad thing about iRay is that it's GPU so to get a good farm you have to spend LOTS of money, the other bad thing is that is being developed by nVidia and it's evolution as a render engine is SLOOOOOW and it's evolution inside max is SLOOOOOWER if it can, and the other bad thing is that it's GPU so it's limited by the GPU Ram... so mooooore lots of money...but speaking about visual quality, that gallery may not be so pretty, but it's more in the artist hand than in the engine hand, you can see not-so-pretty renders made with Corona also, so I think in the majority of the cases is in the artist hand, at least when we speak about Corona or iRay.
And BTW; yes, Bunkspeed is iRay inside a different GUI and they are limited by the Nvidia development speed, they evolve faster than iRay inside max, but they are equally limited to what Nvidia delivers :P
Cheers.