I am working on a leaf shader and the first step in this is creating the shape of the leaf. As you can see in the image below it is then quite simple to add some variation to for example the leaves produced by the Ivy Generator.
The shader and node setups as well as some explantion on how to use the shader with IvyGen are documented in this blog article: http://blenderthings.blogspot.com/2013/01/a-osl-leaf-shape-shader-for-cycles.html
Creating a leaf shape sounds simple but turned out to be quite math heavy (splines, cubic root solving). Those math parts are split off in their own little library (documented in the article) which will be expanded when I enhance the shader to produce leaf veins etc.