So far the consensus on the use of taunt is thus:
When attempting to max it out, just mash the button like crazy.
When using it to retain aggro, use only when necessary. I believe parsing has been done that shows that it puts your hate at the top of the list +1 so it should immediately grab aggro from whoever's got it. Most good tanks (warriors included, and I'm referring to the skill, not good tanking classes) will only taunt 3-4 times a battle. If you're mashing the button, what you're doing is decreasing your chances of being able to pull aggro off somebody else. Most of the time I can hold aggro with my SK through spells and bash aggro but if I lose it I just flip taunt on once and it pops right back. I usually taunt once per fight. I know with my 44 war I never had good luck taunting mobs off with the mash strategy.
I'm sure there's some underlying reason why you also don't want to mash it like crazy. My guess would be is that it lowers your aggro back to +1 of the next person on the list so you have a good chance of losing aggro again, but that's only speculation.
I have also seen instances where I regain aggro even though I failed taunt. That is possibly from bash though.
Hope this helps somebody.