I just finished my basement, using metal studs for about 80% of the framing, including my media wall. I just added 3/4" plywood blocking where the TV mount was destined, and secured the blocking to the studs with PL and Spax screws.
I was able to hang off the mount (about 190 lbs) with no hint of flex or other stress on the wall.
Had I not been able to add blocking, I would have used toggle bolts, as cmdrdredd linked.