So, what do we know so far with certainty for attacks against boss mobs?
Known Hit
8% is the hit cap for ranged attacks, melee specials and white attacks with one weapon.
13% is the hit cap for melee specials with Titan's Grip.
8% is also the miss rate for pets. Focused Aim is acting funny with pets, not granting the pet hit chance if you have little hit rating
It does nothing if you have a significant amount of hit rating on gear. Most likely a bug.
Dodge rate of any attack vs. bosses is just under 6.5%.
Estimated around 6.45%, so you'll want 6.5% reduction from expertise anyway.
Known Crit
Your crit rate for white melee attacks against bosses is reduced by exactly 4.8%.
Unknown Crit
All ranged attacks seem to be reduced by an about 5%.
Crit rate for melee special attacks seems mostly unchanged from your paper doll crit rate. Possibly a 0.6% reduction due to weapon skill difference.
Source
Retesting hit table assumptions
Unknown Hit
What is the hit cap for white attacks while dual-wielding? 27% or 28%, there is conflicting data.
It' is very likely 27% with recent testing.
Paladins seem to get 3% melee hit from some unknown source. Possibly only if they specced into Precision before 3.0.
Judgements count as ranged attacks though, so they need 5% hit for melee but 8% for judgements.
(That is if I understood their threads correctly.)
Glancing/Dodge
White melee attacks have a 24% chance to glance.
Exact average damage is not known to me, but around 75% of a normal white hit.
Dodge chance is higher than 6.25%, but not higher than 6.5%.
Unknown Parry
Ballpark ~13% vs. bosses is all I know.