PROMarker Challenge Blog - a wealth of info and lots of lovely samples, mostly cardmaking but the techniques will surely transfer to stamped images on scrapbooking pages.

Letraset's own site

Lots of PROMarker How Tos on a blog by Wiccababe

A tutorial here (slideshow missing)

From Crafterlicious , some alternative uses (on silver charms, punched acetate flowers, on ribbon)

Two video tutorials here - One and Two (more Anime related but quite good for colouring techniques)