Just wondering. Is it a California only thing...or are people running them because they are easy to install?

Easy to install and 50-state smog legal. I don't live in Cali but I'm trying to keep my 05 pretty much smog legal so I went with the coated JBA's. I am completely happy with them. Definite improvement in power, appearance and under-hood temperature. People have reported gains of 25-30 rwhp with the JBA shorties, but many people don't believe that shorties can give that much. If you get the shorties, I would get the mid-pipes with high-flow cats too. They are good for another 10 rwhp and make the exhaust sound more like a muscle car.