Switchblades are only illegal to sell across state lines. They are legal to own/possess/carry in many states, although your state has the ultimate discretion on this. Around here, they are openly sold at gun shows and the like...a friend of mine sold one to a police officer not too long ago.
With that said, I've turned into a bit of a knife snob and about the only knives I carry are Case CV yellow handle folders(not that they're exactly high end). I have a switchblade or two put back, and in all honesty mine and most of the others I see are really pretty junky knives. The steel is not that good and the overall construction feels flimsy.
The hot thing now are "open assist" knives. There are a lot of companies making these at all price points and with all kinds of blade types. Most are quite substantial feeling, although many tend toward a "tactical" type look/construction. Typically these have a thumb stud or lever that you push to start the blade opening and then the "open assist" mechanism takes over to open the blade the rest of the way(and often quite forcibly-don't get your hand in the way). They are 100% legal at the federal level and I don't think any states take issue with them unless they exceed some arbitrary blade length. Functionally, the only difference between them and a switchblade is that you physically start opening the blade yourself(even if it's only a tiny amount) whereas a switchblade opens entirely on its own. A person familiar with one can open one just as fast and easily as a switch blade-unlike the my preferred old fashioned slip joints, they can be opened one-handed.
Much like the 1934 NFA that banned "gangster" guns, most switchblade laws were targeted at "gang knives" in the 50s. I just don't see a lot of demand for switchblades to return since open assists are just as easy to use.
BTW, around here and in a lot of Southern rural parts of the country, carrying a knife is just something that you do. I have quite a few pocket knives, including several that belonged to each of my grandfathers. With a few exceptions, I keep all my knives(even the old ones) sharp enough to shave with along with spending some time regularly oiling the blades and doing other general maintenance. As I said, though, I mostly stick to recent production CV yellow handles-if I lose a knife I'd rather lose a $40 one that's easily replaceable. I've never even considered my knife any kind of weapon or defensive tool, even though the one I'm carrying might come out of my pocket a half dozen times a day. It's just a general tool to cut stuff, whether it's a open a letter or box or cutting a slice of an apple.