Mobile is a focus insofar as the master-master sync working well for mobile apps where the user may be online most of the time, but offline a significant amount as well. I believe TouchDB is where they're focusing exclusively on mobile now, and it's less of a focus with the main branch.
As for CouchDB vs. Couchbase, Couchbase is a fork of CouchDB headed by CouchDB's creators Damien Katz and J. Chris Anderson. Couchbase basically throws a lot of the nice things of CouchDB out the window (such as the HTTP API) in order to integrate Membase feature.
To be even more specific while still generalizing, Couchbase is the Membase product with a heavily modified CouchDB swapped in for the storage mechanism (previously SQLite).
As for the leaders, it's a smattering of CouchOne/Couch.io and Membase/Northscale people. Or, as a friend put it, CouchOneBase.io.
As for CouchDB vs. Couchbase, Couchbase is a fork of CouchDB headed by CouchDB's creators Damien Katz and J. Chris Anderson. Couchbase basically throws a lot of the nice things of CouchDB out the window (such as the HTTP API) in order to integrate Membase feature.
This is worth reading: http://www.couchbase.com/couchdb