I have had so many folks ask about traveling with knit and crochet supplies. TSA has an entire page dedicated to this topic. Here it is. I recommend that you print this page and should you have any problems when going through security, present them with this information (nicely, of course).
Now, if you are planning to travel abroad, call the airline. Many countries are very militant about knitting needles. I have heard stories of people having a stewardess run down the aisle and almost tackle someone for knitting on the plane. Anyone else have a story to share?