Actually, I see a valid reason for creating another category... Even a lot of postwork (taking out power cables, darkening skies, cleaning trash off of lawns, etc.) still leaves it in the realm of a Photograph. We're talking about added or constructing elements, in which case "Photomanipulation" is a good idea for a new gallery option.

YES, adding elements (3D elements, stock elements, seperate photos, switching elements between images, etc.) immediately makes it modified photography, therefore not a camera original image, but should not be cut-and-dried considered 2D - this is actually a little different and more complicated a situation. It's not as easy as fiction or non-fiction which is a clear black and white issue.

By putting it in "2D" puts it in the realm of drawing and painting. They're almost never viewed the same, and you will hear arguments from those who draw and paint all their work that "it is NOT 2D, thank you very much! YOU just put photos together!" (this is hypothetical, but I can see it coming now)

This is one huge "grey area" and can get a little confusing as to "where" to put your composited image - given that all we have are categories of "Photography", "2D", or "3D software specific".

I propose that if you have 3D elements (ex: Poser characters in front of a background photograph of a waterfall) it should go into 2D. If they are ALL photo elements - highly distorted or not (think along the likes of worth1000.com) - then it should go into Photomanipulation.

What say you my brethren?!
-Lew ;-)