ok guys, i will give you my experiences with chipped ecu's...and this is based on dyno runs and several setups utilizing different chips.
first, remember this: honda ecu's from the factory allow for their motors to run perfectly. this means a p72 running a gsr motor will have excellent fuel curves and make optimum power.
second, too much fuel will cause you to LOSE horsepower. i'm having this problem right now, as my VTEC controller isn't controlling air/fuel as it should be, hence the problems i'm having. with the right fuel curves and 13:1 air/fuel ratio i will probably make between 5-10hp throughout the entire power curve.
third, aftermarket ecu's are designed to run with specific engines setup by the engine builder themselves.
hence, a genuine JUN chipped ecu will run a JUN engine perfectly, so what happens when you just have a b18c5 without any JUN parts...the motor won't be running to its full potential because the fuel curves will be designed for a motor with more aggressive cams and higher compression.
so why do people run aftermarket ecu's? well...some don't look for a knock sensor like a chipped p28 and the redline is higher, which allows for higher revving with motors THAT CAN HANDLE the higher rpm's. so if your valvetrain is stock, and you have a chip designed to rev to 9200 rpm you're setting yourself up for some bent valves and other engine damage.
other reasons for using an aftermarket ecu include increased compatibility with boosted setups, etc.
overall, unless you have a VAFC and plan on dynoing your car IMMEDIATELY, its not worth running an aftermarket ecu that IS NOT designed for your engine. you will either have to TUNE your setup, or just stay with the stock ecu that has IDEAL fuel curves for your motor.