Belt 'n' braces!
Bose sums things up very well - use all the information available and CROSS CHECK. Like the original 3 points of reference to identify a town...
We have 2x 430s installed, so redundancy should ensure that we don't get lost, but we still do a plot, use the wizzwheel and check the notams etc. We have experienced failures with HH GPSs caused by interference from the radios on certain frequencies. Also, the Garmins are slightly slow - has any one else noticed this? There seems to be about 15 seconds delay over a given positive location. This is not too much of a problem at height, but can be significant at low level.
RF