It appears to take 20 uses of berserk to fulfill the berserking prerequisite -- when I acquired wildswing, I was at 20% complete for the achievement "Temper Tantrum". Seems pretty straightforward. Any corroboration?
Yes, I acquired wildswing after 20 berserks on my warrior alt, and have been told the same on (warriors) by at least one other person. I'll add this to the main page. Ducian 17:10, 14 December 2010 (UTC)