If you need to wait for wide adoption in the hosted server market place, this seems like a sensible concern. You can install CouchDB by hand of course, it's really not that hard.

The API changes occasionally, as is natural. The project is improving as we get more popular and people suggest new and better ways of doing things. This is part of having a healthy free software community. It's important to point out that the API is so simple it's crazy, and it changes very infrequently - so it's really not much of an issue.