Anything that says "Minor Run Speed Increase" is 8%.

Worth noting that permanent, base movement speed increases (i.e. not mounted) do not stack. Temporary movement speed increases, auras, activated effects, etc. may or may not stack.

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As an aside, Kruf of Paragon was discussing movement-enhancing effects in Episode 68 of the Hunting Party Podcast as it concerned end-game, progression raiding. To paraphrase, he said, 'Rarely does that little bit more DPS make the difference between downing a boss or not.* More often than not it's getting raiders out of the fire that is going to make a difference.'

The introduction of Worgen was the first time, I believe, he mentioned Paragon had discussed swapping to Alliance for Darkflight due to its raid utility. You can hear the actual discussion first-hand here:

http://www.huntingpartypodcast.com/2011/01/hunting-party-podcast-episode-68/

*I believe he was referring to racials, but it may have been enchants. It's been awhile since I listened to the episode.

Also of note, there is now a "Speed" stat in your character window, its one of the first things and shows you exactly what % of normal run speed you are at, factoring in sprinting, auras, mounts, etc.

Speed enchants bring you up to 108%. Any class abilities (ret pallies, unholy DK's) will bring you up to 115%.