Would be great if the DB ref spec. (http://www.mongodb.org/display/DOCS/DB+Ref+Specification) supported deep referencing.

Perhaps something along the lines {$id:1, $ref:"collection", $namespace:"chairs"}

Also, preferably both support for single embedded objects in an situations where there would be an array of embedded objects. Eg. it should be possible to reference both a single chair and a single roof.

Example:
{
_id:1,
type:"house",
chairs:[ {_id:1, color:"black"}, {_id:2, color:"red"}, {_id:3, color:"blue"}]
roof: {_id:1, material:"wood"}
}