Block is a purely situational stat, which you'll want to play around with most likely. Too much block will probably harm you more than it'll help you against trash due to rage reneration issues. On bosses it'll definatly help, but probably you'll prefer raw avoidance over the mitigation offered by block. I think somewhere around 20% is a decent sweet spot for current gear and content, just remember you can switch around gear to raise/lower that percentage as needed.
As things are now your percentage of block isn't -that- important, what you want to maximise is your Block Value, because that will help you a lot more.