scene graph?

how many people here use scene graphs in thier engine? personally i dont, and i''ve been doing some research, and looking into implementing them, all i can come up with scenenodes are transform nodes, material nodes, and mesh nodes. Then the problem is inserting the nodes? i guess a material would be close to the root, as its the most expensive state change wise, followed by transforms, then meshes... so if a material requires a number of passes, it can set the pass and call the children to be rendered/set. what i have done is the past is just have a list of models, sorted so those models that use the same material/texture are located next to each other... another issue is how to create the nodes from the scene graph, should i ask the scen graph to make them eg: SceneGraph.CreateMaterial( "myMaterial.fx" ); Transform* SceneGraph.CreateTransform(); ideas suggetions link to some tutorials would be exellent ;p