John,

As he's reminded you in a later post, he did say "on the PSU".

I've read it. I didn't want to make a point of it.

I have, however, encountered PCs - I suppose I should really say PSUs -
where there _isn't_ a switch on the PSU itself.

Same here. Just counted: from 9 'puters here three do *not* have such PSU
switches. Thats one out of each three.

But even for the ones that do have them I would not make any bets on them to
work as expected. If there is anything I've picked up when learning to be
an electrician is that assumptions like that will get you killed. Or, in
this case, might kill your motherboard. Pulling the plug and removing
it from the workingspace makes *certain* the power is off, and isn't any
more difficult than using that (rather tiny and sometimes awkwardy placed)
switch. Than again, may'be I'm just a bit over-cautious. :-)

Personally I've not found a case where such isolation has caused a
difference in potential anywhere near big enough to cause harm, but ...

I have. On certain (dry) days just a few steps over the (no doubt nylon)
carpet caused static discharges to occur when reaching for metal stuff like
doorknobs. Repeat 30 seconds later and the same would happen. Luckily I
didn't have to work on a puters innards there. :-)

The "touch the metal frame" was considered always a good thing to do, even
when wearing an earthing wristband. Largely because those tended to bleed
the excess charge off rather slowly (forgot how many megs the series
resistor exactly was), but also doing it automatically could save ones ass
when either forgetting to reconnect the earthing after grabbing a coffee or
simply when, on outside jobs, no earthing point or wristband was available.

Regards,
Rudy Wieser