What my killer app would be? It would be something like this. A tool that helps me when I write emails and documents. It reminds me of related (truly related, not just based on key word comparison) emails, documents (I wrote before), Internet pages (I visited before), etc. in a non-intrusive way.
But for now, the "Shortcuts" are indeed, a good step in the right direction. What "Shortcuts" are? Go ahead and read Iskold's post!