no they aren't really worth it UNLESS you live in a very desert like area with many cacti (if your mountain biking that is), if your not just look at a thicker tube or avoid buying the ultra light tubes as they usually compromise reliability.
Nope. I buy tubes (and just about anything else) from my local bike shop. His price on tubes are about the same or lower than discount stores.
If that's one of those slime or goo filled tubes - don't waste your $$$. They don't really work any better and the slime inside doesn't always fill around equally - throwing the tire way off balance.
