Google Docs (https://web.archive.org/web/20120611101232/http://docs.google.com/?) and Zoho Writer (https://web.archive.org/web/20120611101232/http://writer.zoho.com/?) are web-based writing tools that have gained many of the features of traditional word processors such as Microsoft Word. Looking at Google Docs as an example (Zoho Writer shares many of the strenghts and weaknesses), I wanted to find out if they are mature enough to write a scientific paper.
The major strength is collaboration. All documents are stored online, which makes it very easy for several people to work on a document simultaneously. Because all changes to the text are kept (with author and date), it is easy to go back to an older version. You can import and export documents in various formats, including .doc, .rtf and .pdf.
The obvious missing feature is lack of reference manager integration. Google Docs currently doesn't support footnotes or endnotes, so you can't roll your own references. Google Docs supports font formatting, but unfortunately that doesn't include the Symbol font – needed in almost all scientific documents. And Google Docs online works with an online internet connection, although offline support may come in the form of Google Gears (https://web.archive.org/web/20120611101232/http://gears.google.com/?), Zoho Writer already supports Google Gears.
Google Docs is almost ready to be an attractive tool for scientific writing. Some of the small problems are easily fixed in future updates. The big problem is integration of scientific references. But Google already has Google Scholar (https://web.archive.org/web/20120611101232/http://scholar.google.com/?), maybe the two can be integrated?
For now, Google Docs can help with papers that have many active authors (e.g. a review article), but the final steps still have to be done with a word processor.