I think doing kata is like taking the slow boat to China.
It may be useful when you're sparring in a controlled setting with another KarateKa, but if you tangle with someone who is proficient at jiu-jitsu, or a good boxer who knows how to distance himself properly, or even a smart street fighter, and try to use kata, you're gonna get smoked, and fast.
Not necessarily IF you are taught kata properly it WILL be useful against many attackers including Jujitsu fighters etc. In the Pinan/Heian kata there is double leg take down defence, Naihanchi/Tekki kata can be used as a groundfighting. Kata, need I say any more