I've not used 3D before; having had only Photoshop Standard, and never really having a need for 3D effects.  But I'm experimenting with 3D in the Photoshop CS6 beta, without reading or doing research - just poking around to see what I can do.  I'd call this thing a success, since I've been able to create some quite nice effects just by pointing and clicking.

Since I have no past experience with prior implementations of Photoshop 3D whatsoever, I have absolutely nothing to unlearn, and this implementation so far seems fairly straightforward and discoverable.  But I do have a few first impression observations and questions:

1.  I had to dig a bit initially to find the way to cause the design to render.  I found the Render entry in the fly-out menu, and its associated key combination listed there.  I also finally found the tiny icon at the bottom of the Properties panel.  However, it seems as though there ought to be a "latching" [Render] button somewhere more obvious - maybe up in the Options bar - that you can both push and un-push.  Maybe it should change color to show rendering is active.  It did discover a way to stop the rendering - I just click on the image - but a more obvious button allowing one to start rendering, showing the current state of rendering, and allowing one to explicitly stop rendering just seems missing.

2.  Is there a reason one should wait for the full rendering to occur, if one sees that the result at a given point has gotten "good enough"?  For example, in the image above I stopped the rendering when subsequent passes weren't making any obvious difference, even though the status display still showed something like 80% remaining.  I had left the image zoomed in on one of the letters and its shadow so as to be able make that judgement carefully.

3.  I noticed that the 3D layer returned to what looked like the original "draft" view during design when I subsequently cropped the photo.  Is this because I had not allowed it to complete rendering?  If so, that's a bad thing, since I was quite happy with the partial result and would prefer not to have to wait any longer.  Just this simple design busied my 8 core workstation for a long while!

4.  When rendering, I see that the blue grid indicator seems to spend a lot of time on parts of the image in which there are no 3D objects whatsoever.  Is this because I've inadvertently set something up wrong (ambient lighting?), or does the rendering process just need to re-evaluate the "nothingness" every time to be really sure there's nothing needed there?  It seems like the rendering process could be VASTLY sped up if it just could come up with a bounding box early on and eliminate areas where there is simply no 3D info to be rendered.

-Noel