I'm using the new 3D features in CS6 and am trying to render the 3D elements. I've drawn a marquee around one of the 3D layers ad have set it to render but it seems to be taking forever. Do I need to do this for every 3D layer and what happens if I just flatten the image? My 3D elements have artwork mapped onto them but do not have shadows or reflections.
Depending on what you have created, rendering can take a very long time. You can select just a section of the layer to render to see it work faster.
Since you are having issues with 3d, the most important question is what type of system are you using and with what type of video card.
You need to ensure that your video card is on the supported list and that it has the most current driver.
Check out this link to ensure you have the right card and make sure your driver is up to date. Then, check out the troubleshooting steps.
Please report back and let us know if you still have issues
What are the document specs (bit depth, size, resolution)? What are you machine specs (CPU speed, core count, RAM)? Have you changed any of the 3D preferences?
If you want to render out the 3D layer for an appearance other than what you see in the interaction mode, then yes you'll need to do this for each 3D layer. There are a few ways to attac this scenario and make it more automatic. Flattening your file will remove any ability to further edit the 3D properties, including the ability to render.
While the interaction and drawing of 3D layers generally require the GPU, rendering still only utilizes the CPU for computation. So if it is just the rendering that is "taking for ever" than the GPU update and troubleshooting won't help. You can interrupt the rendering at any time that you feel the quality is good for your purpose, by any keyboard input or mouse click on the Ps interface (we do have a known problem where this doesn't happen sometimes).
Since you don't have shadows or reflections, my quick guess is either you have transparency some where in the materials and/or the machine spec (low CPU core count, speed) is not strong enough to handle the document spec (high pixel count, 300 ppi resolution, 16 bit mode) in a timely fashion.