There is a recently open-sourced fork of CouchDB that does the sharding thing. With this addition to the capabilities, CouchDB really can scale up to hundred machine clusters.
104 karma · joined July 14, 2010
Check out http://www.couch.io/case-studies
And a longer list here http://wiki.apache.org/couchdb/CouchDB_in_the_wild
Remember it's only a developer preview, but it should be fully-functional. Requires Android 2.1 or 2.2
Also, none of the other NoSQLs are really set up for schemaless queries like I am. Incremental map-reduce lets you normalize a bunch of different heterogenous document structures in your view, which is more flexible than the key-path indexes Mongo has, and more real-time than Hadoop/Google style map reduce.