how important is haste for warriors?
 

Specifically for tanking

More DPS more hate.

More DPS does not = more hate, more swings at the mob = more hate. With an FBSS(21% haste) your swing rate with a Sarnak Warhammer (9dmg 20 delay) goes from 30 swings a minute to 36.3 swings per minute. If you add AQ(64%) to your FBSS(21%) then you go from 30 Swings a minute unhasted to 55 swings a minute hasted.

So it doesn't matter how much damage the weapons do? Just get lowest delay possible?

Both wrong and both right. Higher base damage of weapon = higher hate per swing. More swings= more hate. Best ratio is generally what you want but Id ask a real warrior not someone who half knows mechanics. So to answer you, yes you want haste. How this factors in with proccing and the like is beyond me hope this helped some though.

Hate is generated per swing regardless of hit or miss.

Hate generation is weapon damage * 2 + Damage bonus.
Lammy, 9/19 at level 20 generates 9 hate per swing.
Lammy at level 60 with 11 point damage bonus generates 20 hate per swing.

21% haste (FBSS) sets Lammy at 9/16 which is a ~16% improvement in hate generation from swings.

Side note: Haste has no effect on how many times you will proc against a mob (You'll proc the same number of times in an hour at 0% haste as you will with 100% haste as long as your Dex remains unchanged).

Haste is your single most important stat as a warrior. Period.

If you are buying gear you need to balance and can't blow every penny on haste and walk around naked. But your haste item is without question your most important single item.

20% haste is 20% more swings. For simplicty, 100% haste would cut your delay by half, which is twice the number of swings, aka 100% more swings.