So you'll have half as much traffic in 100.5 days? :)
More seriously, this looks awesome. I do all almost all of my writing in LaTeX, including papers, presentations, and random other documents. I've tried to collaborate on LaTeX documents before, but unlike many other types of text documents, the collaboration didn't work very well: the editors that could do collaboration didn't integrate with rapid compilation and previewing, and the editors that do rapid compilation and previewing don't do collaboration.
Have you considered using PDF.js to display the PDF in real-time in the browser next to the LaTeX document? Put that together with something like SyncTeX, and you could show your (or everyone's) current cursor position in the rendered document in real-time. Various tricks also exist to render LaTeX documents more quickly to allow for real-time previewing, such as those used in WhizzyTeX http://cristal.inria.fr/whizzytex/ .
Integration between the BibTeX bits and some form of online reference tracking would make a lot of sense: hit one bookmarklet or browser plugin button on a paper you want to reference, and end up with a new reference in your .bib file.
The biggest question I immediately have: how well does this handle documents that need random packages you don't already have in your TeX installation? From Beamer and TikZ to conference and journal styles to random obscure formatting packages, I don't want to find out in a crunch that I can't easily use any package I need. Do you have any compatibility issues with random TeX and LaTeX packages, perhaps due to the need to run them in a secure server environment? Do I have to add all the individual packages into my project, or can I have them as common elements across my projects? Similarly, can I share my own .bib files and packages across projects?
On that note, what about images and arbitrary data files I might need to include, such as from \includegraphics or
What TeX implementation do you use behind the scenes? TeXLive, I hope?
How do I know what versions you use? What happens when you upgrade? TeX itself might keep backward compatibility forever, but random LaTeX packages don't always maintain that property.
First-impression question: why do you ask for my first and last name, rather than just an email address and password? Do you want it to fill in \author{} automatically? Please say up front what you need it for. Either way, never ask for "first name" and "last name", just ask for "full name", which will work for more people. http://www.w3.org/International/questions/qa-personal-names