digitalartsonline.co.uk have excellent tutorials. Here’s one that shows you how to make a vector illustration from a camera image. It uses both Photoshop and Illustrator and is a good way to experience the strengths of either.
In this tutorial, Eelco van den Berg lets you behind the curtain to see how he creates his incredible vector portraits by turning a photo into a ‘poppy’ vector illustration.
It says that it could take 3-4 hours so you may want to make a cuppa.