Destro is terrible in solo or small group PvP. The only times I can beat anyone solo is if I use every CD, pot, HS, VW sac I can.
Running around a BG, though.. As long as you stay in a big group, you're doing good. You can burn down casters almost as fast as anyone, and shadow priests and other locks love leeching off your ISB that you're much more likely to get than an affliction or demo lock will.
Shadowfury is very rare in PvP, so it's all the more fun to near-instant stun 10 guys. Follow that with an Infernal or howl of terror to increase the screaming of your enemies. You can't get IHoT, but you can at least stun everything around you for most of the cast time.