So to give a little rough example as to why haste is so good for seal of blood.

Lets say you’re using a regular old 3.8 speed weapon with Seal of Blood. You hit with every attack for exactly 1000 white and then 350 yellow.

Example 1: No Haste
Swing Timer: 3.8 seconds
White Attack: 1000
Seal of Blood: 350
DPS: 355.26

Now lets say you get a 150 passive haste rating on new gear (~10% increased attack speed). Your weapon speed now drops dramatically while the damage output remains the same.

Example 2: 10% haste
Swing Timer: 3.42 seconds
White Attack: 1000
Seal of Blood: 350
DPS: 394.74

As you can see, that 10% haste increased your DPS fairly dramatically. It is quite possible to get a very slow weapon (such as TotD) down to a very quick attack speed if you gear correctly. You will be keeping the very high topend damage of a slow weapon, yet hitting very quickly. Thanks to Seal of Blood’s amazing mechanics, its damage scales very well with haste rating.

And just to give a very extreme example, lets say you popped a Haste Potion with all your passive haste gear on. You now have a total of 550 haste rating, which works out to about a 35% attack speed increase.

Example 3: Haste Potion + Haste Gear
Swing Timer: 2.47 seconds
White Attack: 1000
Seal of Blood: 350
DPS: 546.56

Yes, haste can be very nice for Seal of Blood.

Seal of Command (casino) does not scale with haste rating at all because it’s procs are based on a per minute scale. This is one of the main reason’s so many Aliance paladins are asking for Seal of Blood in PVE.

Excerpts from: http://elitistjerks.com/f31/t17193-paladin_retribution_dps_theorycraft/