Read the blocking skill perks, that will tell you exactly how the skill level is applied. Personally I prefer Oblivion blocking in that it can be used when the player wants to use it. Kosh already mentioned Morrowind's method, I wasn't so keen on that, on anything combat wise in general.

Well, TBH, I think all combat skills should be mostly out of the players hands.

As is now, even with low skill you can do really good if you know how to play, when it should depend soley (or mostly) on characther skill.