It would be really nice to be able to blacklist an array of collections that are exempt from replication. It could be an option to the config object for the replica set.

The replica simply would ignore replicating things with this namespace/collection specification.

It would be required to be priority:0 when this setting is active.

This allows for nice trim special purpose slaves to be setup for reporting/analytics/DR or other purposes based simply on a collection basis.

{
			"_id" : 1,
			"name" : "localhost:9002",
			"health" : 1,
			"state" : 2,
			"stateStr" : "SECONDARY",
			"uptime" : 1759718,
			"optime" : Timestamp(1349917851000, 1),
			"optimeDate" : ISODate("2012-10-11T01:10:51Z"),
			"lastHeartbeat" : ISODate("2012-10-11T01:10:58Z"),
			"pingMs" : 0,
                        "blacklist":['test.foo','test.bar'],
                        "priority":0
		},