Others have covered most of it. I paint in "batches" so i can do skin on 5 or 10 guys at a time, then pants and shirts, then belts and accessories, etc... It goes reasonably fast. I also use quickshade/dipping as others have mentioned. I brush on the quickshade rather than dipping, but this tends to cover up mistakes and makes the model look decent. I think I average a couple 2 models a day doing this technique, of course i spread that time out over a long period.
You can see my army in my gallery.
http://www.dakkadakka.com/gallery/user/72079-Loborocket.html
The Ork army there represent about 8 months (on and off) of work or so.