I think the key missing feature is being able to register interest or activity for an idea. It would be extremely useful to see if anyone else is working on an

I think the key missing feature is being able to register interest or activity for an idea. It would be extremely useful to see if anyone else is working on an idea, who they are and what their focus and status is. e.g. When seeing the idea about selling twitter names, it would be helpful for everyone if I could say "Oh yes, Twitter are launching this next Friday" or "Like the idea, have a prototype, need a designer." Comments do help, but a structured solution would make things much easier. Ideally this wouldn't be only first-person, so that people can report other projects which seem similar. You'll need moderation either way (votes or active moderation, whatever.) If implemented well enough, this could breed a sort of communal start-up site. Maybe the originator of the thread gets to choose from respondents and splits equity among them, at which point the idea is locked.