This has already gone around the blogosphere but I shouldn't assume that people that read this blog read the same blogs as I.
I think the first time I truly realised the power of editing in film was listening to the writer/director commentary on Jerry Maquire. Cameron Crowe said that the Tom Cruise - Renee Zellweger story was secondary in his script and during shooting. It was editor Joe Hutshing's rough cut that dramatically altered the story's emphasis and Crowe decided that he preferred it.
It's almost impossible to tell from the final cut of a film just how much the editor did to change the story. An editor may save a film but you'd never be able to tell this without seeing the raw footage. I once asked an editor "how do you judge good editing for, say, the Academy Awards, given that without seeing the raw footage, you really don't know just how much the editor contributed." His response: "you can't and that's the dirty secret of editing awards".
The original post was in the category: filmmaking but I'm still in the process of migrating categories over.