Hey Lyonheart,

Spell hit cap is 17%, minus hit % bonuses for classes if you talent for them. Draenei Shamans with talents can knock 4% and push this down to 13%.

Level Hit Rating Required
1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% 13% 14% 15% 16% 17%
80 26.23 52.46 78.70 104.93 131.16 157.39 183.62 209.86 236.09 262.32 288.55 314.78 341.02 367.25 393.48 419.71 445.94

So the magic number for Ally Shammys is 340ish to hit level 83 raid bosses.

The number should be much lower for heroics, level 82 mobs only get a 6% debuff, so you really only need a flat 158 to hit the cap. Take talents and heroic presence in and a pack of Ally Shamans only need 2% hit = 53! Kinda crazy?

Check out,
http://www.wowwiki.com/Spell_hit