I agree on the images issue. Many other apps, such as some listed above, handle them much more easily and intuitively than OmniOutliner.
Let's not use Apple Mail as a defense as if it's the pinnacle of design and usability or even an analogous type of application.
I'm pretty sure one of the OmniOutliner screenshots shows what looks like image thumbnails:
I'd love to be able to do this- without having to duplicate my images with thumbnail sizes that are then worthless if I want to switch to the quick view.