I personally don't, but I'm thinking about starting to keep my cheap plastic swat-tactical replica on my person from now on. Not really for defense, but it seems like a knife has a lot of practical uses, and I sometimes go riding around at night (bicycle), so I figure it may not be bad to have.
My knife sorta looks like this. I might as well get the real thing seeing as how its only ~$40.

As far as I know, there aren't any laws that prohibit carrying around a folding knife..should I still be concerned?