To see usage sample, you should have a look at the tutorial videos posted on YouTube: http://sites.google.com/site/studioposteffect/videos
Sorry for the lack of information provided bellow.

Create a render plugin

For the ones confortable with .NET languages, you can try creating a new class library project, adding reference to IScenePlugin.dll which is in the root folder of Studio Post-Effect application and create a class which implement the IScene interface. Then copy your dll to plugins folder and restart Studio Post-Effect.

Exploiting data of the project file

Hereafter is the description of Studio Post-Effect project file format.
The project file (.efxprj) is juste a simple xml file, and thus anybody can exploit its data, for exemple creating a converter that generates Ogre Engine compistor files from Studio Post-Effect composition workflows.

Project file sample xml.

In this project file, you can see the "effects" markup, as well as the "textures" markup. These xml containers respectively contain the effects (pixel shaders) and the textures (image such as png, jpeg, etc...). The "file" attribute contains the location of the file relative to the current project xml file.

The most important and interesting part is the "compositions" markup. This element contains all the workflows information. The child items are "composition" containers which are named from Studio Post-Effect application.

Each of these containers stores "items", which are workflow items such as pixel shaders, textures, inputs, output, etc... and "links", which are the links that connect the workflow elements and thus describes the way the composition behaves.
The "items" element stores only "item" child element, and "links" elements stores only "link" elements.

"item" element:
(an "item" element can have only one "texture", "pass" or "primitive" attribute.)

About the "param" elements (child elements of "item" elements representing a pass) :
"link" element:

So in the exemple above, let's describe the workflow textually to ensure the correspondance, in the same order as "link" elements appear :

"The scene is plugged to the first parameter (Horizontal.SourceTexture) of the horizontal blur effect",
"The horizontal blur effect is plugged to the first parameter (Vertical.SourceTexture) of the vertical blur effect",
"The vertical blur effect is plugged to the output (final render)",
"The pattern texture is plugged to the second parameter (Horizontal.PatternTexture) of the horizontal blur effect",
"The pattern texture is plugged to the second parameter (Vertical.PatternTexture) of the vertical blur effect",

As this description shows, the order of the "link" elements as no relationship with the workflow running sequence order.

Workflow obtained in Studio Post-Effect.