Over the weekend we got a new feature in place -- the ability to send direct messages between users. This would have been a great initial feature to fit in, but it wasn't as high priority as some other things. Collaborating through public comments only gets you so far. Being able to exchange messages back and forth can be really helpful in some cases.
Notice also, that developers can choose to produce an app dream (that is, sign on to develop it) by clicking the relevant link in the Actions pane to the right on app pages. This results in the project owner getting a message. The owner can then decide whether or not to add the requester as the producer. Getting the project to this stage is a huge step toward seeing your app made real!
Let us know in the comments if you have any feedback on these or any other features of the site!