Feral doesn't noramlly do well but it's somewhat effective in 2v2 and 3v3. The advantage that feral has is it's burst damage. OoC combined with the highest unbuffed crit % means feral can put out some painful burst damage quite frequently. This is a new aspect of feral though, since S3 replaced the +healing on our arena gear with +crit. This put me in the 41-44% crit range self buffed (I use Idol of Terror, so my crit varies). Even against full resiliance opponents, feral can crit quite often.
The downside is that we have no control over our bursts. This lack of control makes feral druids either a force of pure destruction or a pretty kitty cat.
I do a feral/restro team and we have had success with it. Warrior/Healer groups are usually our biggest problem, other healer/dps groups I can either kill the dps or disable them enough that they're less of a threat. 2 dps groups can go either way, generally I try to kill one of them before they get my partner (no one is going to FF on a feral druid in bear form with a healer). If I can kill one around the same time my partner goes down, then I can use the feral advantage in 1v1 to take it home. Of course I'm always learning and trying to think of ways to counter how that last team beat us. I'm not pro, but I'm satisfied being above average using a sub-par spec.
If you take the time to improve your skills, feral can be effective in 2v2 and 3v3. It's not ideal, and I know that I could get a better rating if I respeced restro, but it's doable if you work at it.