Unable to use IR receiver and motor shield together
If you use the AFmotor library (adafruit shield) with IRremote, there is a conflict on TIMER2 (pin 3). If you do not use pin 9 for PWM issues in AFmotor, you can modify IRremoteInt.h in IRremote library by uncommenting the TIMER1 line instead of TIMER2 like below
... 
// Arduino Duemilanove, Diecimila, LilyPad, Mini, Fio, etc
#else   
#define IR_USE_TIMER1   // tx = pin 9  &lt;--  uncomment
//#define IR_USE_TIMER2     // tx = pin 3 &lt;-- comment
...

On my arduino UNO R3 it works well. With TIMER2, motors 1 and 2 where inactive. With TIMER1 all motors work.
Hope its helpfull for someone else