A super lightweight way of adding and removing Leaflet markers for an Ember ArrayController. I'm currently using it and as it matures I may move it to a repo.

Leaflet.LayerMixin

var Leaflet = Leaflet || {};
Leaflet.LayerMixin = Ember.Mixin.create({
    layerSetup: function(options) {
        var controller = options.controller
        , add = options.add || 'addLayer'
        , update = options.update || 'updateLayer'
        , remove = options.remove || 'removeLayer'
        , self = this;

        controller.get('content').forEach(function(model, i) {
            var layer = self[add](model);
            controller['content'][i]['_layer'] = layer;
        });

        var observer = {
            arrayWillChange: function(observedObj, start, removeCount, addCount) {
                for(var i = start; i < start + removeCount; i++) {
                    var model = observedObj.objectAt(i);
                    self[remove](model['_layer']);
                }
            },
            arrayDidChange: function(observedObj, start, removeCount, addCount) {
                for(var i = start; i < start + addCount; i++) {
                    var model = observedObj.objectAt(i);
                    var layer = Ember.get(model, '_layer');
                    if (layer) { 
                        layer = self[update](model, layer);
                    } else {
                        layer = self[add](model);
                    }
                    controller['content'][i]['_layer'] = layer;
                }
            },
        };
        controller.addArrayObserver(observer);
    },
    // must return the layer
    addLayer: function(model) {
        var layer = L.marker(model['lat_lng']);
        this.get('controller.map').addLayer(layer);
        return layer;
    },
    // must return the layer
    updateLayer: function(model, layer) {
        var layer = L.marker(model['lat_lng']);
        this.get('controller.map').removeLayer(layer);
        this.get('controller.map').addLayer(layer);
        return layer;
    },
    removeLayer: function(layer) {
        this.get('controller.map').removeLayer(layer);
    }
});

// Usage:
App.MarkerController = Ember.ArrayController.extend({
    content: [
        {lat_lng: [35, -90]},
        {lat_lng: [35.5, -90]}
    ]
});

App.MapController = Ember.Controller.extend({
    needs: 'marker'
});

App.MapView = Ember.View.extend(Leaflet.LayerMixin, {
    didInsertElement: function() {
        var map = L.map(...
        this.set('map', map);
        
        this.layerSetup({
            controller: this.get('controllers.marker'),
            // specify custom methods for handling layers. Defaults to "addLayer"
            add: 'addMarker',
            update: 'updateMarker',
            remove: 'removeMarker'
        });
    },
    addMarker(model){
        // return the layer so Ember can track for when it's removed
        return this.get('map').addLayer(L.marker(model['lat_lng']));
    },
    updateMarker(model, layer) {
        //...
        return theUpdatedLayer;
    },
    removeMarker(layer) {
        this.get('map').remove(layer);
    }
});