One thing to be careful of is that a 960px screen does not mean you have 960px to play with. For example, a common screen width is now 1920px. A lot of people will have two windows side-by-side, so each window is 960px wide. But that 960px has to include the browser edge/border and the scrollbar – you may only have 940px of actual screen real estate to use. So your carefully crafted site that is exactly 960px wide is now too wide, the edge disappears off the side and your reader has The Dreaded Horizontal Scrollbar.
That's why 960 is a bad width to work to.