We're running the latest stable version of Mongo (1.6.3) compiled from source and it is definitely stable (we're running 4 shards, 2 servers per shard, 2 config

We're running the latest stable version of Mongo (1.6.3) compiled from source and it is definitely stable (we're running 4 shards, 2 servers per shard, 2 config servers and a bunch of arbiters plus mongos on all of our servers that access the DB). I don't necessarily think stable and actively developed are mutually exclusive.