Thomas Mayer wrote:
> Dean
> 
> ESD can vary between 200 volts and 2,000 volts. If the computer case is 
> not grounded, there is a risk that the charge could reach some internal 
> electronic computer components before dissipating into the atmosphere. 
> And, once the power supply itself is turned off, there is no electricity 
> reaching the internals, but the remaining connection to a grounded 
> outlet provides a ground for the case. Of course working in the power 
> supply itself is an exception.

There are even specially designed computer cords (usually colored in a 
primary color) that only connect the ground plug to the AC outlet.

http://www.cyberguys.com/templates/searchdetail.asp?productID=5338
http://www.cyberguys.com/templates/searchdetail.asp?productID=5339

The main reason I recommend users unplug is that not all power-supplies 
have a disconnect switch on the back of the PSU.  Also, not all ATX 
motherboards include a "power LED" that shows whether the motherboard is 
still receiving power from the PSU.

(Different approaches and different valuations of risks.  I had one user 
swapping memory on a live ATX system because they didn't understand that 
just because a unit is powered off doesn't mean there's still juice on 
the motherboard.  Fortunately, it did no damage.  But the system was in 
a very confused state and would not power back on until I cut the power 
by pulling the plug for 30 sec.)

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