Array.observe() should be specified in more detail with respect to sorting an array. In recent versions of Chrome the code snippnet below indicates that its current implementation of Array.observe doesn't scale well when it comes to sorting. There are a lot more change records generated than there are elements in the array. As it seems there's an update for each permutation. I think there should be just a single "update" change record after sorting, where "name" refers to a pseudo property 'order'.
Example:
{
type: 'update',
name: 'order',
object: [/sorted (orig. reference)/],
oldValue: [/* unsorted (reference to clone?)*/]
}

// i = 9 => changes.length = 54
// i = 9999 => changes.length = 143499
var x = [];
for (i = 9; i >= 0; i-=1) {
x.push(i);
}
Array.observe(x, function (changes) {
console.log(changes)
});
x.sort(function (e1, e2) {
if (e1 < e2) {
return - 1;
}else if(e1 > e2) {
return 1;
} else {
return 0;
}
});