Personally, I'm still using GPS as my backup to check my visual/radar
fixes (which I consider to be more "real world" true) until all Charts
have been corrected using GPS/DGPS readings.

Bingo!

I've been lurking on this thread waiting for someone to bring up the
key problem with GPS: sure it's mighty-fine accurate, but it's just a
lat-lon, *useless* until related to navigational features of interest
somehow, usually by consulting a chart, electronic or paper. If the
chart is not on the same datum and is also mighty-fine accurate, then
the *chart* is the weak link in the GPS/chart system of navigation.

And charts are accurate at best to a pencil width or two at the
original scale of the chart. Blowing the chart up by a factor of a
thousand on yer super-fancy GPS chartplotter so you can see your slip
makes that pencil width turn into maybe 200 feet, even on a detailed
harbor chart. A pencil width or two on an approach or regional chart
can turn into a half mile or more. So that's the level of accuracy in
a best case scenario for the GPS/Chart system.

Problem is charts are just a faint shadow of the real world:
Cartographers miss things, misplot things and mislabel things. Some
things can't be accurately plotted, some deep-set buoys can swing on
their moorings by a half mile, for example. Charts are not real-time,
as they age, changes occur in the real world which don't magically
appear on the chart. Charts are on many different datums, for example,
if you don't have the brains to switch your GPS receiver datum from
WGS84 to NAD27 when you switch to a NAD27 chart, up to 500 feet or so
of error auto-magically appears in all your plotting. Charts are
necessarily incomplete; other ships, massive breaking waves, flotsam,
commercial fishing gear, etc., don't appear on them. And, if you're
sailing in out of the way places on the planet, the chart, although
pretty, could be a P.O.S., positions off by miles, inconsistently; and
show things which didn't exist a the time of survey and omit things
which did.

The result of thinking your GPS is accurate to a few feet when you're
actually using GPS/chart system? Disaster! On a cruise in the Sea of
Cortez last month we anchored a half mile inland in a few spots,
transited breaking shoals, saw islands to port pass to starboard; all
according to our color big screen GPS chartplotter with a fresh chip.
Every year here in Southern California several powerboats run up on
Huntington Beach at cruising speed, because they zoomed in to San
Diego Buoy #1 on their whiz-bang GPS/chartplotter, set a waypoint,
panned to Angel's Gate in Los Angeles, set a waypoint, created a route,
locked in the autopilot, then went below and hit the sauce. Problem
is that route grazes land halfway through the passage! I'm sure you
can come up with your own stories; and I've got a few of my own where
I've been surprised by taking the GPS picture as gospel.

What GPS has done is allow nitwits to navigate right on the money, most
of the time, and not develop other navigation skills. Used to be
natural selection took care of them sooner or later. Cruising's going
to hell, a high-tech solution to every problem: sail handling? -
roller furling!, water? - watermaker!, batteries? - battery monitor!,
navigation? - GPS! All very alluring, but harsh mistresses when they
go south.

Now, radar, depthsounder, RDF and the Mark I eyeball and earball are
not derivative navigational tools; there is no lat-lon fixed scale
chart accuracy correct datum ju-ju going on. They have their problems,
but on a good day you are directly relating the real world to your
position, no third parties - satellites, master control stations and
cartographers involved. And, as you "zoom in", i.e., get closer to the
thing in question, accuracy gets better linearly, unlike zooming in on
a chartplotter. It's much better to know that navaid in the fog is
actually-right-now 200 yards off your starboard bow than to think the
sexy picture on your chartplotter is reality (which has it off your
stern).

That being said, I'm a multi-unit GPS owner too, mighty useful, but
it's more of a glance now and then and autopilot brain for me. Good
for detecting current and leeway effects, where the GPS is essentially
calculating a vector between where you are now and where you were a
short while ago, no chart referencing there. Good for calling BS on
your chart, if the Mark I's are telling you a different story. Really
good for returning to the *exact* same spot where you've taken a GPS
waypoint previously, or relating your position to another vessel's
reported GPS position (if they're dialed into the same datum). Super
accurate clock, too.

But it's no magic bullet, because of the chart problem.