I have been working a little on a style in TileMill, using my laptop. The screen is 1366 x 768, so squeezing the display in is a nuisance. The TileMill page would be a bit better if the two main panes were able to be sized. The 1366 x 768 screen is now the most common screen size for a PC, so support could be better, maybe a tabbed layout might be better. The documentation is a bit sparse, but I have found my way around without too much hassle. Downloading the osm-bright example helped a lot. It is by far the easiest way to I have found to create a Mapnik style.
TileMill uses Mapnik to render the images and so Mapnik2 was installed as part of TileMill. I installed python-mapnik so I could run Mapnik stand-alone from a python script. TileMill offers to export the Mapnik style and I used that to make an image file.
Well, it should work, and it did. It was simple to do and I now have a style that I can use in Mapnik to render various places with my own style.
Now I can work on the style confident it will work.