As someone who used to write a lot of LaTeX documents, this just isn't up to snuff yet. It's slow (which they can fix) but what would make it really helpful is hints in LaTeX commands and support for packages. I haven't tried any complex documents yet, hopefully a full 200 page doc with biblo and index would render correctly as well. It's cool though, I hope it does end up working well.
There is a full TeXLive distribution on the back end, so all of the packages are there (including beamer, tikz, bibliography, etc.). The editor is CodeMirror, so the underlying infrastructure for auto-complete is there; I just haven't had a chance to try it out. I mostly use writeLaTeX for short documents (papers, talks, etc.), so I've never tried it with a 200-page document -- current page limit for the auto-preview is 30, but that's a bit arbitrary.
