Here is a suggestion. Instead of having to go back to the hundreds of posts and add an image and a description for Pinterest, what about a slight change allowing this plugin just to grab the featured image and the excerpt (either automatically generated or from the already-existing post/page form)?
It would make things so much easier :)
Also, an add-on to add the Pin-It button to the ever-present Jetpack/ShareDaddy would be cool.
Just a suggestion; if this is completely contrary to the spirit of this plugin, I might develop my own hehe — I just take a loooooong time writing code!