Seems like there's an incompatibility between 2.0 mongod/2.1 mongos on sharded mapreduce.

To repro, replace 2.1 mongod with 2.0.4 mongod and run features2.js, results in :

ri Apr  6 15:59:00 exec error: src/mongo/shell/collection.js:661 map reduce failed:{
	"ok" : 0,
	"errmsg" : "MR post processing failed: { assertion: \"invalid parameter: expected an object ()\", assertionCode: 10065, errmsg: \"db assertion failure\", ok: 0.0 }"
}
throw "map reduce failed:" + tojson(raw);

Attached sample output (there was some additional spurious logging in the mongos in this output, but reproducible in multiple other tests).