Currently, fast tanking weapons affect paladins as well as it can give them more chances to proc their seals and judgments. This is assuming that the above mentioned are not affected by an internal cooldown. I know that seal of Vengeance / Corruption isn't and the faster the weapon the faster it will hit it's full stack. And that does actually affect threat gen more than you would think.

well, i guess that's true for threat if you're using seal of righteousness, but most tanks use seal of corruption/vengeance. while true that a fast weapon will stack SoV a little bit faster, once it's stacked, the damage comes from a dot not affected by weapon speed, and a proc using 33% of the weapon's damage, also not affected by weapon speed (faster means more, smaller procs so it's a wash). seal of wisdom is on a PPM system, and presumably seal of light is too, so that too doesn't really favor fast over slow.

About the only thing 'fast' does for a paladin is speed up the SoV stacks (although that's mitigated, too, since Hammer of Righteousness stacks SoV, too). Otherwise, slow is better, threatwise. All because of seal procs; everything else that a prot paladin does (currently) doesn't use weapon damage or speed; it uses attack and/or spellpower, block value, or Weapon DPS. But seals are normalized by weapon speed, one way or another. Back when they were only procced by auto attacks, this meant that speed didn't enter into it. Now, they proc off instant attacks, too, and weapon speed doesn't affect how many of those you get. Slower weapons = bigger seal hits on instant attacks, too.

It's probably worth pointing out, too, that Hammer of Righteousness demonstrates that Blizzard has the technology to make weapon speed largely irrelevant for instant attacks if they want to; when it first appeared it did the more common "x% of weapon damage," but was changed so tankadins wouldn't avoid fast tanking weapons.