As mentioned elsewhere, I usually only work with acrylic paint on paper when I Illustrate my books, however, I have also (mainly as an experiment) produced three books using Photoshop Elements 3.... and I love it!
To keep the digital work as close to my hand-painted work as possible, I make a strict point of working only in one layer and using only one 'brush'....very primitive considering the array of wonderful tools on offer! I just change the size of the brush now and then, depending on wether I'm drawing or painting. To add a little texture I sometimes switch over to ArtRage 2.5 but the main body of each illustration is strictly as described above.
These illustrations are from a book called "You are what you are!" (Du bist Du! in German, Je suis comme je suis! in French, etc.). 
Although I consider myself a paint & brushes type of painter, I have to admit that working on the computer certainly has its attractions. Some people seem to think that it's somehow cheating, or taking an easy route but... for me at least, it's often much harder work than painting by hand! 
In any case, I hope you enjoy looking at the illustrations....