Up until now I have mostly tried to steer clear of block rating and block value, because I didn't really think it was worthwhile when tanking bosses, I mean taking 1500 less damage from a 20k hit didn't seem worth it. As you can see if only thought about the defense capabilities of block value, and not the offensive ones. And now I've read multiple things about block value being very important for threat upto a certain level, whereas I have tried to gear for threat by getting hit and expertise so far. I have also seen on the new paladin tier 9 tank sets, that they carry a lot of block value with them, and that pretty much discouraged me a bit, but perhaps I was mistaken. Up until now I haven't really had threat problems in raids yet, but I am wondering if I should start gearing for block value since it seems to be such a good stat.
The short answer is no, you still want avoidance over block. Block Value has always been nice to have, even before the changes in 3.2 as it adds to your threat/DPS and mitigation. The problem is, Block Value almost exclusively comes with Block Rating as well, which very quickly becomes wasted as you gear up (most Paladins find that they reach the block cap raid buffed without really trying).
I'd definitley recommend having a block set for when you're tanking trash or for something like Thorim's Arena as you can make their damage all but completely trivial but for your MT set we're still pretty much looking at Effective Health and Avoidance being king.
On a semi-related note, gear with Expertise on it is now more attractive than it was in 3.1 due to the fact that the new Seal of Vengeance swings can be parried and nobody likes being gibbed by parry haste. Don't gem for it, but look twice at gear that has it, basically.