I have good news and bad news for the casters in the group! Let's start with the good news.
The Good News
Prior to the 3.0 patch (which prepared us for the WOTLK expansion) there was a built-in one percent miss chance for any spell you cast. That means, at most ninety-nine percent of your spells hit when you cast them. The 3.0 patch removed that very small chance to miss
The Bad News
Casters must now make up that extra one percent chance to miss to achieve maximum raid efficiency.
So, for the offensive casters (Mages, Shadow Priests, Elemental Shamans, Balance Druids, and Warlocks) you need to achieve 17% total hit rating to never miss a target up to 3 levels above you--such as a raid boss. Since it takes 26.23 hit rating (at level 80) to equal one percent hit rating this would mean you'd need 445 hit rating to never miss.
But it's not that dire. Every offensive caster class has skills in their trees to increase hit rating. For instance:
- Druids have a Tier 6 Balance Talent (Balance of Power) that will increase their chance to hit with balance spells by 2%
- Mages have a Tier 1 Arcane Talent (Arcane Focus) that will increase their chance to hit with arcane spells by 3%
- Mages also have a Tier 2 Frost Talent (Elemental Precision) that will increase their chance to hit with frost or fire spells by 3%
- Priests have a Tier 2 Shadow Talent (Shadow Focus) that will increase their chance to hit with shadow spells by 3%
- Shamans have a Tier 6 Elemental Talent (Elemental Precision) that will increase their chance to hit with their spells by 3%
- Warlocks have a Tier 1 Affliction Talent (Suppression) that will increase their chance to hit with affliction spells by 3%
- Warlocks have a Tier 2 Destruction Talent (Cataclysm) that will increase their chance to hit with destruction spells by 3%.
The Alliance has even better news in store! Draenei have a racial skill (Heroic Presence) that increases the chance to hit by 1%, so if you're a dwarf, gnome, human or night elf that will always have a draenei in your group, you can let your hit percentage drop to 13% (14% for Druids) to a mere 341 hit rating (368 for druids). Be warned this is A LOT of hit rating to go for especially pre-raid gear. Trust me.
And where is all that hit rating going to come from? Well, consider foods, gems, and enchants. They will all significantly boost hit rating. But where it all comes from is a topic best saved for another day.