Ok, this time, inexperienced as I am, I don't agree at all...
GPS mis-loading errors are easy to detect by using the moving map to zoom right out and display the whole route, before setting off.
I prefer to check leg distances from the entered GPS route to leg distances from the plog. Easier to see "minor" but significant faults that way, IMHO...
A GPS without a moving map is OK for a door stop, nothing else.
Not at all! The moving map on something like a KLN89, or even a GNS430, I find rather useless... The KMD550 is the smallest unit I find really useful (I suppose a GNS530 is also large enough to be readable). On the other hand, I find the other functions on the GPS extremely useful, from the off-track indications when a route has been entered, to getting a quick bearing and distance to the airport when using direct-to. On the KLN89 I don't even bother using the moving map at all, yet I love that unit.
Actually, I would be perfectly happy with a GPS that featured only three functions:
1. A continuous readout of the current track
2. A continuous readout of the current groundspeed
3. A switch with which to turn the thing off in case of electrical problems
That is enough to take the crosswind problem out of simple map, compass and plog navigation. Even if I'm not using the GPS for anything else during a flight, I always use it for that: When turning to a new heading, first turn onto the planned magnetic heading from the plog; compare the GPS track to the magnetic track that I also have on the plog; adjust compass heading until GPS track matches plog track. Then it's back to looking out the window.
And I don't need a moving map to do that!
Also a good idea to plan the route on VORs or NDBs, and tune in the navaid, for an enroute cross check.
Can do that anyway; select "nearest -> VOR" on the GPS, tune in the VOR on the radio, and ensure the indications match (but I would agree this is more useful for a DME than a VOR, and even worse for an ADF). That way you can cross check indications whenever it is most convenient, without having to plan based on radio navaids.
That said, it is much harder to mis-program a GPS than to "mis-program" a VOR. On the latter, setting a track of 180 v 080 etc etc is easily done if in a hurry. In the goode olde days, pilots (including commercial ones) had little idea of where they were most of the time, other than when right on track to/from a navaid. We have an easy life nowadays.
If flying VFR, you'd often use waypoints that are not in the GPS database, wouldn't you? That means adding user waypoints manually, whether by place/bearing/distance or lat/long. Lots of digits to enter, in the usually awkward knob-twisting manner, and lots of possibilities for error.