Well, Rachel's post just reminded me of a great illustrator I discovered when I first joined twitter, Lynne Chapman. She too illustrates strangers on her train journeys.
I love the changes in the quality of her line work, as well as the wonderful added colour and writing. It reminds me of some of the tea and crayon's ladies actually!
I hope you like these too, I find them rather inspiring! It shows that practice makes perfect. I think I may try to carry a sketchbook around always, I want to improve my observation skills further!