The startup warnings printed:
https://github.com/mongodb/mongo/blob/master/src/mongo/util/version.cpp#L176

...don't match the recommendations in the documentations for ulimits:
http://docs.mongodb.org/manual/administration/ulimit/

...or the recommendations in the Production Notes:
http://docs.mongodb.org/manual/administration/production-notes/

My suggestion: add warnings/ notices in the logs (and warnings on the command line stdout or stderr) anytime a setting doesn't match the documented recommendations.

Ex: "[notice] Your open files system ulimit (value) is currently below our recommended settings. You can read more about that here: http://docs.mongodb.org/manual/administration/ulimit/"

Another example: "[warning] Your replicaset has an even number of nodes, which may prevent it from electing a new primary in case of a server failure. You can read more here: http://docs.mongodb.org/manual/core/replication/#architectures"