Can MongoDB do master-master replication? Oh, it's can't, and really only CouchDB does in the NoSQL space? Oh, that's too bad. Of course, most of us don't NEED M-M replication, as it introduces serious issues with reliability (oh I wrote the client record to server A and then queried server B on the next page load and it didn't exist yet -> Null Exception #AWESOME!) and is only useful for backups/reporting/import/export scenarios. The rest of us who actually want to GET WORK DONE will probably continue with relational DBs and post JSON documents as needed into our databases (e.g. json doc for lists/complex objects where we don't want/care to index any fields within).
And ACID doesn't fall apart at all in sharding - what are you smoking?? You implement a standard sharding scheme and the same record always goes to the same server. NoSQL doesn't do a thing for sharing... Replication is a problem, but it is for NoSQL too.