I would like all of my users to be able to read and write to the datastore very quickly. It seems like MongoDb has blazing reads, but the writes seem like they could be very very slow if the one master db needs to be located very far away from the client. Couchdb seems that it has slow reads, but how about the writes in the case when the client is very far away from the master. With couchdb, we can have multiple masters, meaning we can always have a write node close to the client. Could couchdb actually be faster for writes than mongodb in the case when our user base is spread very far out geographically?
I would love to use mongoDb due to its blazing fast speed, but some of my users very far away from the only master will have a horrible experience. For worldwide types of systems, wouldn't couchDb be better. Isn't mongodb completely ruled out in the case where you have users all around the world? MongoDb, if you're listening, why don't you do some simple multi-master setups, where conflict resolution can be part of the update semantic? This seems to be the only thing standing in between mongoDb completely dominating the nosql marketshare. Everything else is very impressive.