Hit cap can be a real pain because of the various numbers thrown about.

For Spells
Level 83 mob (?? boss mob) - 17% chance to miss
Following pulled from warlock guide:

17% = 446 spell hit rating (rounded up)
14% = 368 spell hit rating (this assumes +3% from talents OR raid buffs)
13% (alliance only) = 341 spell hit rating (this assumes +3% from talents OR raid buffs, and +1% from draenei racial)
11% = 289 spell hit rating (this assumes +3% from talents AND +3% from raid buffs)
10% (alliance only) = 263 spell hit rating (this assumes +3% from
talents AND +3% from raid buffs AND +1% from draenei racial)

For Melee

This is where your 8% number you heard came from. This is the cap for 2-handers and I believe main hand when duel wielding.
Special Attacks are the same 8%
Off-hand is 27%

Some Melee have spells that use the same spell cap of 17% spell slingers use.

Allesarelle