Personally, I'm not a big fan of knifing - but that's just cuz I keep getting knifed! Always seems like it's right before I nail that long range sniper shot, lol!
In all seriousness, I love the BF franchise, but I've never had much success in melee situations - seems I'm always on the losing end of them. I tend to just flail about while the other guy pulls out his pistol and shoots me in the face. Otherwise, I don't have any issues with the knifing system in BF3.