Just for the record, the only way to get full CTC in MoP against raid bosses is getting 104.5% block, which is unlikely to happen at any point except possibly during occasional procs. So this addon won't be quite as useful as it has been during Cata, as the caps won't be hit.

Mob level: Required to get full CTC
Level 90: 100% block or 97% dodge + parry (3% miss)
Level 91: 101.5% block or 101.5% dodge + parry (1.5% miss)
Level 92: 103% block or 106% dodge + parry (0% miss)
Level 93: 104.5% block or 109% dodge + parry (0% miss)

[Removed warning not to use on Live realms, as 5.0.4 has now launched so this addon is once again ready for live usage.]

If anyone wants to double check my math, please feel free. MoP is doing some "fun" changes that really tweak the way the combat table has worked since 2004 (block formula, miss chance, avoidance changes per mob level above you).

The percentage you are aiming for really depends on what level content you are doing. If you are raiding, 102.4% is the goal (each defensive stat [miss, dodge, parry, block] is reduced by 0.2% per level a mob is higher than you [3, for skull-level bosses], thus 4 * 3 * 0.2% = 2.4%). If you are only doing heroic 5mans, the highest mob level you will see is 87, and thus 101.6% is your cap. But yes, the higher the percentage, the lower the chance you have of taking full damage from a boss's "hit," and thus higher is better.

Like the GearScore controversy in Wrath, note that higher isn't strictly better, as you should take into account what type of avoidance/mitigation it is that is getting you there. Replacing 2% parry with 2.1% block is a higher CTC percentage, but you will likely take higher damage overall (as parries are full avoidance while blocks are only partial reductions). Plus if you are a warrior you may be sacrificing potential Hold the Line uptime.

If you reach your cap, block will be the first stat to be pushed off the table, so switch to increasing dodge or parry (with the removal of the defense rating stat, chance to be missed is no longer able to be increased, except by race/faction changing to Night Elf).