Their app, Kaleidoscope (http://www.kaleidoscopeapp.com/), sounds to be an incredibly simple app to make. Not that I am planning to make yet another app like that, does someone know if it's selling well?
In the fluid mode, the text on the two panes need not be of the same height given the insertions and deletions. So when scrolling, the scroll speeds for the two panes would need to be different. Is this what is being talked about?
I do not have a Mac, so cannot try it myself.