Don't throw them out. There are a number of things you can do with them.
1) Get some contrasting fabric (say, plaid) and patch them FROM THE INSIDE. Use a three-step zigzag to fasten the edges down from the inside, use a thread that blends in to the denim (a pale blue). That way a bit of plaid showing through is a fashion statement. YOu can edge the rip with lace & pearls but the pearls would be uncomfortable to sit on.
2) Cut them off right across where the rip is, then sew it shut. Insert a zipper in the waistband and use a strip of fabric form the legs to make a long shoulder strap. You now have a stylish shoulder bag, complete with handy pockets for your iPod, mobile phone, etc.
3) Keep the old jeans for patching other old jeans. Whenever I make "sawn-offs" I keep the legs to make denim patches. You can also unpick old denim and make denim patchwork with it. The advantage of old denim - you can use it to patch old jeans. YOu should never use new fabric to patch old.
I love using 3 step zigzag, it is almost invisible when you use it to sew on patches. The first patch I did that was designed to show the hole, was husband's army hat ("giggle hat", that khaki bucket hat that Aussie troops sometimes wear). They'd been on tactical drill under fire and as a whiz-bang went overhead, he threw himself to the ground and his hat flew off, landing right over the whiz-bang. The resultant damage to the hat was spectacular and husband didn't want it hidden under the patch; but we had to sew something onto it, to stop the fabric (what was left of it) from fraying. Mind you, I also had to wash out the sweat and gunpowder...
Marg