block value also increases Shield Slam damage and threat generation (SS is instant, with a CD, where as HS is a 'next swing' attack.).

With full sheild spec warrs get another 30% (I think Pali's also can put points into this talent).  I can block for around 350 DMG per and I dont even that all that much BC gear yet ...  I know other tanks can block around 400 and up, so its pretty key when the boss is crushing you for 2K per shot (and more).

Blocking also seem to work on some ranged attacks as well...

I can crit  for over 1K DMG with my blocking gear, its not a lot, but then you realize my shield does that much damage, it really aggroz those mobs :)