MultiKey sorting example

coll = db.foo
coll.drop()

coll.insert( { arr : [ { a : 1 } , { b : 2 } , { c : 3 } ] } )
coll.insert( { arr : [ { a : 2 } , { b : 3 } , { c : 1 } ] } )
coll.insert( { arr : [ { a : 3 } , { b : 1 } , { c : 2 } ] } )

coll.ensureIndex( { arr : -1 } )

coll.find().min( { arr : { a : 5000 } } ).max( { arr : { a : 1 } } ).forEach( printjson )

is the find possible form the ruby driver at all? I read the source of the driver and was unable to see how its possible to run the fins with the min and max functions

Yes - its just using $min, $max under the hood.

Is there anything else I can do regarding http://groups.google.com/group/mongodb-user/browse_thread/thread/578c6d037d241162 ? I am at a loss of how to get this working.

Looks like you didn't follow the example.
Notice the ensureIndex has a -1 rather than 1