gistfile1.js

//1.5.4
> db.test2.insert({
...     name : "Something",
...     things : [
...             {foo : "148091a0719c", bar: 1},
...             {foo : "0026080741c6", bar: 0}
...     ]
... })
> db.test2.update({name:"Something","things.foo":"148091a0719c"}, {$set:{"things.bar":2}})
can't append to array using string field name [bar]
> db.test2.update({name:"Something","things.foo":"148091a0719c"}, {$set:{"things.$.bar":2}})
> db.test2.findOne();
{
        "_id" : ObjectId("4c3e99f0460b000000007ab0"),
        "name" : "Something",
        "things" : [
                {
                        "foo" : "148091a0719c",
                        "bar" : 2
                },
                {
                        "foo" : "0026080741c6",
                        "bar" : 0
                }
        ]
}

//1.4.4
> db.test2.findOne();
{
        "_id" : ObjectId("4c3e99f0460b000000007ab0"),
        "name" : "Something",
        "things" : [
                {
                        "foo" : "148091a0719c",
                        "bar" : 2
                },
                {
                        "foo" : "0026080741c6",
                        "bar" : 0
                }
        ]
}
> db.test2.update({name:"Something","things.foo":"148091a0719c"}, {$set:{"things.$.bar":5}})
> db.test2.findOne();
{
        "_id" : ObjectId("4c3e99f0460b000000007ab0"),
        "name" : "Something",
        "things" : [
                {
                        "foo" : "148091a0719c",
                        "bar" : 5
                },
                {
                        "foo" : "0026080741c6",
                        "bar" : 0
                }
        ]
}