I carry a knife anywhere I legally can, except work, usually. Not as a weapon though...like most of the posters here, I view knives as very useful tools that CAN be used as a weapon if needed.
That said, I tend to carry a liner or axis-type locking blade clipped in my strongside front, back or cargo pocket depending on clip configuration and what I'm wearing. I like CRKT and Benchmade (They have a nice line of "budget" folders) as well as my trusty Spyderco Rescue.
Have I ever used it as a weapon? No...thought I might have to once or twice, but always a false alarm. Use it as a tool? Pretty much every day.
On a side note, I do like folders that protrude from my grip some when still folded...something that can be used as an impact weapon if needed without the blade open. I like having options