Depends on what you do really. The kung fu I learned was very traditional, but also very self-defence based. Everything we did in forms had to work in practice. But yes, alot of classes are sport-based, although most systems can be taught either as sport or self-defence. When I teach self defence, it's pretty much a case of learning how to survive when attacked - i.e. by out-violencing the violent attacker. My classes generated many complaints about the violent techniques I taught, but people who have been to my/our classes and been attacked have got out without injury - regardless of whether they damage the opponent or not. And yes, I teach people to rip, gouge, tear, pull, twist, prod, stab and poke - not a single punch! I also teach the first rule, which is avoidance: ie make sure you aren't out alone in dodgy areas, and you get a lift if you can etc, you cross the street if you see trouble, and don't broadcast what you know. That's normally enough to save your bacon.
As far as weapons goes, it's a funny one. The average hooligan attacking you with a weapon is actually pretty good if you are trained - since you know they will attack you with the weapon - they are using it to intimidate you. However, if someone skilled attacked you with a weapon, you probably wouldn't know too much about what happened - you'd see the knife when it is in you. but then again, if it was someone that good, then you have probably got yourself in deep, deep trouble, which is bad self-defence
If someone attacks you and fails, then you are the winner, and that must be your goal.
So as far as learning martial arts to defend yourself goes, take it on a club-by-club basis - not even style by style. I've seen some appaling kung fu classes where people cannot fight, but then I've seen classes from systems renowned for not being applicable to self-defence full of double-hard b**t**ds who I would NOT mess with.
Then there's the rise of MMA - mixed martial arts, like Jeet Kune Do, Keysi, Vale Tudo, Pancrace, Krav Maga etc, which are quite simply applied violence. Go there to learn to defend yourself! But for some reason, the classical grounding in traditional MA will always help you out - studying your posture and getting grounded in the longer stances does wonders for the legs and the root, and helps in generating power. I always find people with a classical base do better in those systems for that reason.
Long answer - but that's my opinion.