I come to this discussion late. I too come from the radio range days/SBA/Consol/Loran/Sun Gun/Decca/Doppler etc etc right through to triple INS and Omega.
In my current day job, we use 2xGPS with UNS1K FMAs as the primary BRNAV requirement. It works very well.
It is categorised as RNP5 equipment. This means that for 95% of a flight, the equipment is guaranteed to keep the aircraft within 5 nms of track.
My fun aeroplane is equipped with a Garmin 430 which I love but when I am crawling round the London TMA, I assume that even if it is as good as the kit I use in my day job, it is only guaranteed to the above limits. I therefore try to give everything a miss by at least 5 nms just in case I'm in the 95% of the time and not when the error could be in excess of 5 nms for 5% of the time if you see what I mean!
Looking out of the window helps enormously.