I think I've maybe used shadowfury once or twice, just to test it out. Wasn't impressed.
Also, if you're doing 25-man Naxx and your SoC doesn't explode almost instantly, everyone else must either not be targeting the mob or everyone's DPS is far too low for any lvl 80 content.
My aoe of choice is usually RoF, due to no cast time. SoC has a cast time, which in 10 or 25 man groups, trash get cleared pretty fast. SoC isn't very helpful in those situations, imo, due to the mobs are pretty much cleared by the time you get 1 SoC cast.