How to shutdown op-amps for low-power standby
Maybe. You have to realize that the inputs (or even output if there is a pull-up) may power the op-amp through protection networks. If that is not an issue, then a high-side (eg. P-channel) MOSFET or PNP works fine. Some op-amps allow inputs in excess of the supply voltage, which is nice when your supply voltage is zero.
Depending on your application you may wish to consider an op-amp that has a power-down input. That allows the Vdd to be maintained, but puts the amplifier in a low power consumption mode.