For me, knitting is partly an experience like Amber's - I am not one to sit idly and watch television or just look at the scenery on a car ride. I used to read obsessively, but I concentrate on that so deeply that I usually don't hear what's going on around me, which drives the men in my life insane!
So, now I knit...when I'm not working or blogging or on this forum or cooking or shopping or just "Being Mom"!
You see, I have two sons, ages 12 and 19, a hubby, a bunch of pets, a couple of friends and *their* pets borrowing my spare room for various reasons, and a very busy, very high-stress job. My DH and older son both have ADD, and my younger son is just, well, 12! So, I always wind up having to be the brain in the family, in addition to the stress of my job.
So - knitting is part relaxation, part keeping me from the inanity of watching TV, and part creative outlet. And a lot of pride in producing something to keep someone warm or make them feel pretty or something.