[dmuino]

I agree that the biggest issue is #1. Another problems I've run into are:

- Operations are not automatically aborted if the client closes the connection. Suppose a case where the client is sending many queries that are queued by the server (usually waiting for a lock to be released). Client times out, re-establishes a connection, retries, etc. Mongo will execute the operations even if the client is no longer waiting for the response. Operations are not automatically aborted.

- Sending slaveOk() queries need to be sent to the slaves explicitly by the driver, and I haven't seen it work reliably. Ideally you'd send them to mongos and let it send slaveOk() queries automatically to the slaves. All the drivers would be simpler and just work. But this is not the case. You can't do it unless sharding is enabled. Each driver needs to implement this functionality.

But I must say that overall my experience has been very positive. It's very developer friendly. You can go from not knowing anything about it to having a working prototype in an hour or so. The flexibility in querying the system is awesome.

You just need to understand the limitations of the system. Once you start pushing the limits it gets significantly more complicated.