I carry a knife for everything but SD, really. I use it 5 10 times a day for little chores, and it is a daily part of my dress.
I say I don't carry a knife for SD for a few reasons, but what I should say is that it isn't even close to being a primary reason. This is true for a few reasons, the first being that I doubt, very seriously, that I will ever be in a position where I am going to have to shank someone. Knives specifically designed for self defense aren't as handy at other tasks. If I really need too, I figure any of the three knives I rotate between will be enough.
Add to that the fact that I am a pretty big guy and plenty capable of popping someone in the teeth with a degree of authority. I've no qualms about battering someone, and that would be my first response. Stabbing someone is pretty much a last ditch, kill or be killed line of defense for me.