Good topic. A little bit of this subject is covered in the Torture thread, I think. You may like to look there as well.
I think the amount of violence contained in one's writing should be measured by how much is really necessary. If I were writing a battle scene that I wanted to be as authentic as possible, a lot of violence would probably be essential to making the writing tangible. In this case however, I would not make the violence the focal point of the writing, but merely describe as the scene progresses. As a soldier would probably glance around a scene of war and take in the sights, would probably be how I would display it in writing. Brief snatches of descriptions here and there, not dwelling on a specific target or going over it in explicit detail.
However, if it is necessary for the plot's sake to go into detail - such as, the soldier dying a horrific death was the MC's best friend - then a bit more gore would probably be required to add to the realism and emotion of the scene.
A lot of violence isn't something I have had a great deal of practise writing, but those are a few of my thoughts.
I also think it depends who your audience is. So if you're writing for adults you could put in more violence than if you were writing for children.
Body parts are not supposed to come off, so that often bothers me. I really have not read very violent books, though. What I've read is the Torture Thread. 
So, I'm sorry, but I can't think of any real specifics.
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