As said, ball soaking is a "big" DPS loss (rogues with cloak/pallies with bubble etc can't dps meanwhile), while having a single tank running around doing it during cleave phase is far less in terms of lost uptime etc.
Don't be afraid to use cooldowns like Aura Mastery on the implosions - it's largely useless for anything else (blood rage is physical), so we personally (with 3 paladins) used AM on the 5th and 6th implosion in set#1, and on 4/5/6th in set#2 (where he does 25% more damage).
Things like Spirit link and void shift sadly does not work to give someone more HP. It's lost untill bloodrage begins and you can heal up again.
Don't be afraid to use healing CD's to top off people's shields at the start of each phase - the seismic slam goes out almost instantly, and if the shields aren't full, that HP is lost for the next 2 minutes.
Each phase lasts 2:50 seconds - which means you can't repeat the same cooldown rotation for #1 and #2. EG, if you barrier for the first 10 seconds of the first Bloodrage. it won't be up untill the last 10 seconds of the second Bloodrage. Do not be chaught off-guard by this. You will have to have a more extensive CD rotation than normally.
Windwalk totems gives immunity to the root effect during Blood Rage, and you get 2 sets of debuffs going out every bloodrage. This means you want atleast 2x shamans of any type to drop these, one per debuff, so you don't have to move the entire raid (assuming you stack for blood rage, of course).
Indeed. It is quite confusing <.<.
It's Blizzards own definition of it - the fact that they can't be bothered to add "true" damage to distinguish between effects reduced by it, and effects that aren't, is pretty damn annoying though. But if you look over the Armor tooltip ingame, it clearly states "Reduces Physical damage taken by XX.XX%" - that's what we get to work with, so that's where I'll start off with my assumptions =P.