I agree with Mark on this one, they often gain the headline BHP increase by raising the rev limiter, which is obviously not good for engine wear !
If your car is 2003, surely this will invalidate the warranty, OPC's are pretty cute ! Also could affect your re-sale, I wouldn't want to buy a car thatbhad been chipped.
Best solution wait until you are ready to upgrade, then treat yourself to an "S", yes I know it will cost you more than a chip, but you get a lot more (uprated chassis, brakes & more goodies, as well as more grunt) & will get a lot of the extra back come re-sale.