I like it! There are two things I would still like though. One would be page rendering in the browser. We often have to iterate several times on a paper adjusting figures, text, padding, etc. to get everything to fit within the page limit. I could write the paper in this and then export it to tex, but that defeats the purpose. The second thing is support of popular LaTeX packages. It looks like I can upload arbitrary tex documents, but that's going to get messy if I have to upload the same packages for every paper I'm writing.
We use github for our papers right now. Less than ideal. "