I try to use only open collector to ground output devices with an on board pullup resistor so as not to chance injecting any high voltage spikes on any pins. Hall Efect Switches are much better than mechanical ones as there is no contact bounce. Watch for the ones that source or have PNP outputs as the source of there voltage is the source of there supply. If placed a resonable distance from the PIC input pin lines become great antennas. Most all of my designs however use opto isolators for digital input to elimnate these problems. Even with Hall Efect Switches.