I've just seen a screenshot of Ulyesses, which is a interesting piece of software mostly targeting novel writers. But I doubt only fiction authors are in need for such software. It makes the management of large texts with different subsections easy to handle, and since you are very restricted in the layout it, you won't spend too much time in breaking and repairing it. I try to write as much as possible using Kile, which makes it also very easy to navigate through your text. But in research you never write alone, which means you write most of your stuff in OpenOffice/MS Word, and you share only *.doc files. It's slowly changing, which makes me thinking about the perfect text writing environment for me. Here are some requirements:

• Collaboration is not a matter of sending the edited full document to my collegue and waiting for a response. A document is usually divided in many different sections, and each section should be handled individually by the system. An obvious solution is to use a VCS like Subversion, and split (internally) the document into many documents. Each author can check out the section he is currently working on, and saving means automatically to upload the section again. Real-time collaboration would be of course even better.
• In my case drafting a text always starts with mind-mapping, and it is always tedious (and kind of unnecessary) to keep mindmaps and resulting texts synchronous. UML editors with round-trip engineering show how it works, why don't we have it for texts also? I should be able to link sections in my text to nodes in the mind map (or even concept map), and switch between the two views easily.
• Layouting text should be very simple. Since we are only talking about a simple editor, we wouldn't need, for example, the whole citation support. Or different styles for headers, indentions, footnotes, ... You can simply add this at a later stage.
• Collaboration does also requires annotation facilities. Collegues should be able to comment on my text, suggest changes, and so on. OpenOffice / MS Word support it, and I, well, can't stand it. It's much to intrusive, a soon as I see a document opened in MS Word with "Track Changes" activated and hundreds of changes listet on the right side, each with a line pointing to highlighted section in the text, I feel the urge to press the "close"-Button.

It actually doesn't feel to hard to find. The software exists, it's just a matter of putting it all together using the right toolkit. Let's see ;) ...