It really isn't customed for me to block with a weapon, but I can vouch that it is a life saver at times. Usually, if you attack then backaway and block, the worst that can happen is you take some damage and get guard broken, but a block can usually sustain 1 hit before being broken. The problem, of course, will be dealing with combo attacks.
It really is nothing amazing, unless you are using a UGS, which is surprisingly decent at it.
A note about blocking with a two handed weapon: Most weapons have crappy hit resistance, but since you're holding it with both hands it's actually higher than it looks on the stat screen.