I think smacking or locking the child in his room is a bit extreme, and therefore should only be used in extreme circumstances. I think the most important thing is to give the child a very clear message that temper tantrums are not the proper way to get what you want. The kid should get the exact opposite of what he wants if he has a temper tantrum. Raising a child is all about teaching him/her how to behave like an adult, and one of the most important lessons is that you can't always have everything you want, and some ways of trying to get your way are much better than others.
I agree that aurorach133's friend should probably think about switching rooms with her son, but I imagine that will not fix tings instantly. I will also give her the benefit of the doubt and assume that she has tried the night light, stories, etc.. It seems obvious to me that this boy is used to getting what he wants by having a tantrum, and this is the main problem! The mother should not have to go to bed at 8:00 just because her son won't sleep without her! To me, this situation does seem extreme mainly because the boy has been getting his way through temper tantrums for 7 years. Therefore, I think an extreme measure is appropriate to begin mending this situation. Once the child understands the temper tantrums will not get him anywhere, then the mother could start to talk to him about his feelings and try to compromise, and I think compromise is the key word. Ultimately, I'm sure the boy wants to sleep with his mom every night, but you can't always get everything you want.