Attached Link: http://www.theli.net/TMP/PP.jpg

For me, I don't like to limit myself to a single utility to create my fractals. Instead I'll try out several programs (non-fractal ones) to have them create or render fractals. If this is postproduction though, I'm not sure. :)

Most of the time, the postproduction I do use is for frames to my UF renders. I find that I can create much better frames in Photoshop than in UF, so I'll use Photoshop. No questions asked.
Most of my fractals has more or less been postproduced, often to enhance details, create depth, add textures or even starfields, color or level changes.
I often tend to render my UF fractals as .PSD so I can alter them later in photoshop.

Here is a fractal I rendered with the intention of using postproduction. PP in this case involved lighting, color, deleting of details and adding of texture.