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).