Here is a "warm up" image composition I created in a couple of hours, using two images I downloaded off of stock xchange and a few other photos I took myself, and a bit of painting.
Definitely fun stuff, and doesn't take all that much time really compared to assembling an image from scratch in a render program...
I've found composited images tend to work best with a bit of pre-planning, and good source image quality and type (especially matching light angles). Then its just a matter of assembling the image based on your plan, matching the colors/contrast, painting/cloning the required areas to blend edges, and then post processing the overall result for the mood.
