Suddenly, everyone disappears. Was it something I said?
This is the biggest challenge of any project; keeping people interested, willing, and able to contribute. While I understand the usefulness of Google Docs for editing (we use it a lot at work), it is also possible some don't have Google accounts they want to use for this. As well, it is often easier to hack at/edit things that are a little more developed. While getting input at the start is always valuable, many may not be sure quite where to begin or where they could best contribute.