When it comes to rendering, I would say good photorealism is 75% lighting and environment. You could take an average model, toss it into Max and it will look bad. Throw in a HDR, and the average model begins to look very realistic. Same applies to an outdoors photo - take an overcast day and take a photo, it will look alright. The subject remains the subject. Take the same photo on a different vibrant day, and the photo could look 100X better.
I would probably say that most of the best 3D photorealistic artists are also pretty good photographers or have a background in understanding photography. From talking with them, I know that Peter (over at Chaosgroup), Lele, and Zuliban are very much into photography.
What I am attempting to say in a nutshell is that lighting and environment are probably the most single important aspect (beyond a rendering engine) to creating a very good scene. Of course, I am not an expert in these areas, but I think they would agree.
I thought some of you would find these photography videos handy:
(1 of 8 ) http://www.youtube.com/watch?v=6lsRu90jE88
(2 of 8 ) http://www.youtube.com/watch?v=9crGU-QRCZE&feature=related
(3 of 8 ) http://www.youtube.com/watch?v=VUJ\_nV4UXcQ&feature=related
(4 of 8 ) http://www.youtube.com/watch?v=eMY\_uWZRNEg&feature=related
(5 of 8 ) http://www.youtube.com/watch?v=B4PK7gddT\_s&feature=related
(6 of 8 ) http://www.youtube.com/watch?v=sJugEUrqCH4&feature=related
(7 of 8 ) http://www.youtube.com/watch?v=t49wbabsM5E&feature=related
(8 of 8 ) http://www.youtube.com/watch?v=9oFWgGIWRRM&feature=related