> db.foo.insert({x:1})
> db.foo.findAndModify({query:{x : 1}, update:{$set : {date : new Date()}}})
{ "_id" : ObjectId("500f0966afa3600a3d3fdcd8"), "x" : 1 }
>
> // this should return {"n" : 1, ...
> db.runCommand({getlasterror:1})
{ "n" : 0, "connectionId" : 7, "err" : null, "ok" : 1 }
> db.foo.findOne()
{
        "_id" : ObjectId("500f0966afa3600a3d3fdcd8"),
        "date" : ISODate("2012-07-24T20:45:28.665Z"),
        "x" : 1
}