Here's what i read on WoWWiki:
Hit refers to physical damage that occurs as a result of an attack made with melee or ranged weapons. The chance to hit increases by 1% per 15.8 hit rating points at level 70 and 10 hit rating points at level 60. The base chance to miss with maximum weapon skill against an opponent of equal level is 5% for two handed and 24% for dual wield.
Calculating Miss Rate for Physical Damage Attacks
Hit rating decreases chance to miss rather than increases chance to hit. Chance to miss in PvE is determined solely by the difference in the defending mob's Defense Skill and the player's Weapon Skill. Further, the effect is not linear. So, there are actually two different formulas that might apply, depending upon whether the difference between the mob's Defense Skill and your Weapon Skill is greater than 10 or not. Here are the two formulas:
If the difference between the mob's Defense Skill and your Weapon Skill is less than or equal to 10 then the formula for calculating your base miss rate against that mob is:
5% + (Defense Skill - Weapon Skill)*.1%
dual-wielding: 24% + (Defense Skill - Weapon Skill)*.1%
If the difference between the mob's Defense Skill and your Weapon Skill is greater than 10, then the formula for calculating your base miss rate against that mob is:
7% + (Defense Skill - Weapon Skill - 10)*.4%
dual-wielding: 26% + (Defense Skill - Weapon Skill - 10)*.4%
Applying these formulas gives the following base miss rate for a Level 70 character with a 350 Weapon Skill:
* v. Level 70 mob: 5.0% / dual-wield: 24%
* v. Level 71 mob: 5.5% / dual-wield: 24.5%
* v. Level 72 mob: 6.0% / dual-wield: 25%
* v. Level 73 mob: 9.0% / dual-wield: 28%
Thus if you are a Level 70 character with a Weapon Skill of 350, you need a Hit Rating of 142 (9.00%) to never miss a shot against a Level 73 boss (or skull mob).
What this means is that there is a big +hit benefit to keeping your Weapon Skill within 10 levels of the mobs you are trying to fight. For example, by improving your Weapon Skill from 340 to 345, you effectively reduce your chance to miss against Level 71 mobs by 3%! However, after getting to 345, increasing your Weapon Skill the next 5 levels, to 350, only reduces your chance to miss by an additional.5% (or 3.5% in total). Also, note that there is a huge jump in miss rate reduction by going from 344 to 345 Weapon Skill. This is the point where you switch from one formula to the other, and so this particular single point of Weapon Skill is worth a dramatic +1.4% hit against a Level 71 mob.
Pre 2.3, racial bonuses provided +Weapon Skill, and thus turned out to be pretty valuable for improving your +hit capability. For Humans, Dwarves, Orcs and Trolls their racial bonuses increased their Weapon Skill at Level 70 from 350 to 355. With a 355 Weapon Skill, your base miss rate against a Level 73 mob (or skull boss) was only 6% instead of 9%.
...So i guess it is 9% base miss...i always thought it was 5% for a mob your level and then 1% for each level higher than you.
Edited, Dec 3rd 2007 11:48am by chood