We've been working on a group communication app which uses CouchDB as the backend. It's called Sharegrove http://sharegrove.com and we couldn't have done it without couch!
In addition to the CouchDB back-end, we've built a custom framework in Java and server-side Javascript (using Rhino) to handle authentication, application logic, and comet-y messaging. The unique thing about our framework is that the app is written almost entirely in Javascript, and portions of it are delivered directly to the browser. So couch is a perfect fit: in some cases we run the same function in our app that we do in the database! The biggest challenge we've faced with couch is the trouble it has with 2nd order relations. For instance, in order to figure out which of a user's groups have the most recent comments, we first fetch all the groups that the user belongs to, and then we get the update times via a POST request to a different view. But overall couch is awesome, and I also want to say thanks for all the help we've gotten from this list. We're starting to see traffic pick up on our site, but our CPU utilization remains almost nil. I'll hope to see some of you on http://sharegrove.com! Best, Adam Wolff
