I've followed the CouchDB project with interest over the last couple of years, and see it is now an Apache Incubator project. Prior to that, the CouchDB web site was full of do not use for production code type disclaimers, so I'd done no more than keep an eye on it. I'd be interested to know your experiences if you've been using CouchDB either for a live project, or a technology pilot.
Answer
After 18 Months of prototypes, testing and waiting for CouchDb to get ready we moved an internal application over to CouchDB in December 2008. So far I'm very happy with that move. It gets rid of a lot of filesystem objects for us (PDFs and JPEGs, now stored as attachments in CouchDB). This enables us to get rid of NFS and easier cluster/replicate our frontend webservers.
To what degree CouchDB is ready for you depends very much on the culture of your organization. We have an in-house development team maintaining several internal Erlang applications. Since CouchDB is written in Erlang and the codebase is of quite decent quality we felt confident that we could fix show stopper issues in CouchDB should the need arise - or at least get our data back out. We also hired one of the CouchDB core team as an consultant - just in case.
But CouchDB for sure isn't 1.0 yet. There are crashes in the Web worker processes all the time (if you misuse them). Replication breaks for us and we don't get error messages about it. Documentation is still very lacking. Still I'm confident that it will not eat our data and development moves forward with reasonable pace.
To give you an idea about our application: currently our biggest database is about 512000 records taking 7.5 GB of diskspace.