mack - 10:39 am on Jan 2, 2013 (gmt 0)
Its not so much the occurrence of a word, but the power of the word within the content. You could look at it as a percentage.
There are however a lot of factors to take into account. A word in a heading will carry more value, titles will carry a lot more value and text that stands out will also have more value when it comes to density.
Don't make the mistake of going all out go really boost your keyword density, this will only lead to an over optimisation penalty.
Carry out searches and see what sites rank well. Go over their source cone and note down occurrences of words and where they are placed.