I, personally, have found no use for Block Rating as a tank. Assuming Mark/Kings/HoW or SoE, I have 29% Dodge, 19% Parry, 13% Block, 545 Defense and 41k HP with Fort, food and flask. My block value in 4/5 8.5 and 8.0 Shoulders is 1244 without Libram or the 4 set proc and I do just fine when the guild needs me to take over MT spot.
You definitely want Block Value on your gear for threat-heavy fights like Hodir Hard, but you can avoid Block Rating imo because it's only useful on fast but weak bosses and trash. Sometimes I don't even Holy Shield just to make it easier for RNG to hit my 30% Dodge, which was something debateable that I brought up with one of our guild officers and we're currently discussing in a think tank on our guild forums.
Don't get me wrong, I do Holy Shield, but it's the last thing I want to do. With dps pushing 7k on normal bosses and the rest of them between 5-6k, I'm much more reluctant to blow the GCD for Holy Shield over hitting yet another threat ability. Right now, none of the tanks in my guild touch paladin threat, and this is not just the Hodir fight. My main concern is keeping threat off of the locks and mages that we have pouring threat out through their eyeballs, at least until Invis and Shatter are fixed in 3.2

Figure it this way, I can tank General without even touching Holy Shield and minimize threat issues throughout the entire fight. Blocking 2.1k dmg on a spike will not save me when there's a rolling Rejuv, disc bubbles, sacred shield, 2 Dodge trinkets, Scorpid or IS glyph, Sanc and other mitigation effects. I can survive two full hits from General's normal melee swing before dying (45k hp full raid buff and 28k armor before Inspiration) without a problem. Healers on me would be using the exact same heals as they would if I did Block the damage, and my dps can go balls out...
Formulate your own conclusions, but I say they just get rid of Holy Shield and give us a more useful cooldown (Redoubt is enough, just make it passive already, jerks...)