[sanmiam]

Depends on the car and the setup. Putting it on the cold pipe would be a better way to do it IMHO because it accounts for the pressure drop in the intercooler, but it can be done either way. As for the boost thing:
IDLE = low RPM's, very little exhaust gas, turbo not spooled, very little boost
WOT = high RPN's, much more exhaust gas, turbo spooled, much higher boost