I don't really reccomend them as a warm-up either simply because they are a great compound exercise that can be used to gain some good mass and strength. I like doing them as heavy as I can (added weight) and will also give them a fairly high priority in my workout on chest/tri day. Usually I do them as my second or third exercise while I am still fairly fresh to get the most out of them.
I do them as my first tri excercise. I think it's best to do them when you are freshest, meaning the first tri excercise as opposed to last. Definitely not a warmup excercise.
If your doing them first warm-up the elbows really good. They put a lot of stress on the joints but I too think there one of the best exercises for chest and tri's.