Ross nails it! Every app (spreadsheets, SAP, wordprocessors, iMovie, iPhoto, iDVD, etc.) that can create any kind of content (text, video, audio, etc.) should have a "Save to blog function" that uses the MetaWeblog API today and the Atom API (when it's ready; unfortunately it is not ready today!). Heck "Save to Blog" should be an API built into the operating system just like "Save to File" is.
From WebGrabit v2.0 Imagined:
There is one last bit that would make WebGrabit a killer app for me - give it a "Publish to Blog" function that would allow me to take any bit of text from the WebGrabit RSS Desktop Component, format it, edit it, add to it and allow me to save it directly to Random Bytes as a weblog post.