Unless you're going omniscient, head hopping in a single scene is bad. Whenever you approach a scene, you should decide who is going to be the most interesting perspective to see things through, and then stick with it. There are some instances where it's necessary to get multiple perspectives out of the same scene, but in this case you should probably write the same scene several times over from different perspectives, without really retelling the scene over again in the same way. Obviously if the perspective is omniscient then this isn't an issue, but unless your entire book is omniscient, you should almost never switch to that perspective. The only exceptions I've experienced where this was okay was when the author took a step back from any of the perspectives, and instead talked about the world or a large location.
For instance, if Bob is about to bring his army to Castle Mountain Dew, and rather than wanting to tell the story from any specific character's head, you just want to give the general feeling of what's going on in the village about to be attacked, then switching -- briefly -- to omniscient to describe an old woman going into her underground shelter, then to a family boarding up their windows and barricading their doors, etc. That sort of thing is usually okay in moderation.
Anyway, if you're not going omniscient, and you're not approaching your story like Quentin Tarantino, then you should approach every scene from the most interesting, and most relevant character's perspective possible. Switching up to another point of view in the middle of a scene just so that we can know ahead of time that Jackie is about to pull a knife is pretty lame and unnecessary.
