Originally Posted by Engine

I think most people casually accept "no problem" but I personally think it sounds crude unless you've asked somebody to go above and beyond their normal call of duty in which case they may say "not at all" or something.
I guess it's generally acceptable as a laid back alternative to "you're welcome" in everyday life.
In a professional setting, however, saying "no problem" translates to "Dude, I'm still just a kid so this is the best way I know how to say you're welcome." So if you ever have a job where you regularly talk to clients that spend a lot of money on your services you'll quickly learn not to say "no problem" when they thank you.