I did use SoV in a duel once. I'm Holy Pally dueling a Holy Priest. First round, I chucked on all my spl dmg gear (this was before 2.3 patch)and thought I'd whale in and whack him. BAD IDEA!. Don't really do enough damage to use that tactic, by the time I got through his shield he had feared me and was slowly smacking me up from a distance. I eventually lost.
Second Round, change of tactics. I threw on my full heal gear. Fight started and all I did was throw on SoV and start hitting him. He would do his usual fear, holy fire etc... I was in my heal gear so a couple of FoLs and I was back at full health. Meanwhile, my couple of stacks of SoV had eaten through his shield. This continued for a good 5 or 6 mins until the priest ran out of mana. I still had over half of mine left since all I did was FoL when needed and cast SoV a few times. So..... Holy Priest with no mana... I went on full nuke (well as much as a Holy Pally can nuke :p) down in 30 secs.
This also happened in the 3rd and 4th rounds.
So... this is completely useless unless you are fighting a holy priest who doesn't know how to adapt to different tactics.