There is a 5% base chance to miss vs a mob of equal level to the player.

Thus a lvl 70 player (assuming max weapon skill) with 0 hit rating, attacking a mob of lvl 70 will miss 5% of the time.

Current end-game bosses are considered level 73 for purposes of hit/resist etc.

For the next 3 levels, there is an additional 1% miss chance per level.
Thus lvl 73, the miss chance is 8%.

There is more though, every 1 point in defence gives 0.04% additional chance to miss.
3 levels = 15 points. 15 x 0.04 = 0.6

So miss chance vs an end-game boss is 8.6%.

I play Hunter so I'm not bothered about melee but as I understand it, Dual-wielding increases miss chance right? If I'm right (not sure about this) then it is probably worth getting more +hit than this.

Druids don't have an offhand weapon attack, this is a big part of rogues needing so much hit, talents being the other part. 24% base chance to miss with offhand. A druid does only need about 5-6% to hit.