<sigh> As expected in the patch, Blizzard have apparently fixed the FFB bug with elemental precision, which was giving 6% hit instead of 3%.

So... new hit caps and things which affect hit caps, pinched happily from someone on the forum who'd done the calculations already:

" 17% without any talents against level 83 mobs (raid bosses)
6% without any talents against level 82 mobs (heroic bosses and some trash)
5% without any talents against level 81 mobs (mostly trash)
4% without any talents against level 80 mobs (mostly trash and players)
6% less with two maxed hit talent and using arcane spells (elemental precision AND arcane focus and only using arcane spells)
3% less with a maxed hit talent (elemental precision or arcane focus depending on the spell)
3% less with a boomkin OR shadowpriest in the raid (doesn't stack)
1% less if you got a draenei in your group

Hit chance needed. Hit rating needed.
--------0%--------------------------0
--------1%--------------------------26
--------2%--------------------------52
--------3%--------------------------79
--------4%--------------------------105
--------5%--------------------------131
--------6%--------------------------157
--------7%--------------------------184
--------8%--------------------------210
--------9%--------------------------237
-------10%-------------------------263
-------11%-------------------------289
-------12%-------------------------315
-------13%-------------------------342
-------14%-------------------------368
-------15%-------------------------394
-------16%-------------------------420
-------17%-------------------------446


TALENTS
Elemental Precision in the Frost tree increases your chance to hit with all spells by 1% with each point, to a total of 3%.

Arcane focus in the arcane tree reduces your hit cap with arcane spells only by 1% with each point, to a total of 3%. Arcane focus stacks with Elemental Precision and with both maxed you would have a total of +6% hit with arcane spells and +3% with fire and frost.

DEBUFFS
Improved Faerie Fire, Misery. If you are in a group or raid with a shadowpriest or moonkin you can assume that they will apply one of these two debuffs to the target. They provide a debuff on the target that increase that chance that you will hit the target by 3%. Improved Faerie Fire and Misery doesn't stack with each other, but they do stack with all other ways of improving your hit chance.

RACIALS
All draeneis have the aura heroic presence that boost the hit chance of themselves and everyone in their group (not raid) by 1%. This stack with all other ways of improving your hitchance. The usual raid-setup on the alliance side consist of 1 draenei pr group (and the group with most healers missing if only 4 available). If you are horde you do not have an equivalent of this buff available.

GEAR & FOOD
Unlike the above these two sources of boost to your hit comes through rating rather than a fixed percentage. The conversion between hit rating and hit percentage change depending on your gear, but for level 80 the following applies:
1% hit increased chance to hit =26.23 hit rating"