OmniOutliner for iPad Review at Macworld
If you make excessive use of outlines, as Jeff Carlson does, you’ll appreciate the ability to build and edit them on the iPad. It’s often a more convenient method of jotting thoughts that can be expanded later on the Mac without having to pull out your laptop or wait until you’re back at your desk. In this review for Macworld, he touches on the advantages and depths of OmniOutliner for iPad, as well as a few surprising limitations.
Does it have Dropbox capabilities?
It doesn't. The Omni Group has said they don't plan to add Dropbox as an option. I'm not sure why, but my suspicion is that they don't want to rely on a third-party company to host stuff like that (even one with a good track record), in favor of their own iCloud implementation. Or perhaps it has to do with how records within an outline are synced. (Clearly, I'm not a programmer, so I'm just guessing.)