Hello!
I work for an Arch Vis firm and we use FormZ and EIAS exclusively for our 3D needs. I’ll just list a few of the pros for you relating to Arch Vis in EIAS.
- The Global Illumination is blisteringly fast and excellent quality.
- EIAS handles ridiculous polygon counts with ease (we’re talking tens of millions here).
- Camera (the EIAS render engine) produces fantastic images in a short space of time, this is mainly due to its exceptional anti-aliasing and Hybrid Phong-RT rendering.
- Unlimited renderfarm licences. Yes, you heard me, there are no network rendering licences.
- Great animation tools (the Function Curve Editor is a thing of wonder) and EIAS has built in scripting ability through Xpressionist, a plug-in that comes with EIAS.
Now for my two gripes about EI and Arch Viz (I’m going for balance here 
- Even though Raytraced reflections and transparency are extra speedy, Raytraced soft shadows are not the fastest on the market (which is what we expect from EI!).
- We don’t have an RPC solution for 2.5d or 3.5d people instancing. Yet. However we manage with 2d or 3D people for our animations.
That said, the benefits hugely outweigh those gripes (that are more then made up for by the speed of other areas).
Take a peek at some of our selected work from over the years (including some questionable inclusions
at http://www.watsonassociates.net
Also take a look here http://3dworks.com/code/frameset_e.htm for some more EIAS Arch Vis images.
Finally, I met an EIAS user in a bar last week, and he had recently been forced to switch to the program and render engine you mentioned by his new job, he said to me that, the image quality they provide is simply not a patch on Camera. He had had a few though 
Ian
PS. Plus all the stuff that Brian said!