The PulseIn example shown here: http://www.arduino.cc/en/Reference/PulseIn
needs a note to use a digital pin on the Arduino Mega instead of pin 7 as shown in the example. Pin 7 on a Mega is an "analog in" pin and the example code does not work using pin 7 on the Mega.
There are two pins 7s on the Mega. One of them is an analog pin, and won't work with pulseIn.
The other one is a digital pin, and will work with pulseIn.
I agree that the pulseIn page should probably clearly indicate that it only works with digital pins, however it does talk about HIGH and LOW which are digital pin terms.
You can use the analog input pins as digital pins with the aliases A0, A1, etc.