As stated above, imo it has less to do with nodes but everything to do with the "weight" of the scene and how much the renderer has to do in each bucket (a single hi-res head with hair closeup can max you out fast). Generally, if the render stops somewhere and you can X and clear it, it's a bucket size issue and reducing it will eventually get your render. If it locks up during a render and the only way out is the task manager then, it is one of many other problems...usually an overburdon on the memory (mine at least), or the poser/devil who says Hah! You did not save first....