I run a ground probe in all of my tanks, with all electrical appliances being ran through a GFCI protected power bar. If a piece of equipment leaks stray current, there is no risk to my fish, or myself, as the GFCI will kill the power source & I will immediately know that I have a problem somewhere, and can rectify it.
Another perspective, from an electrical engineer.
http://joejaworski.wordpress.com/2007/09/06/aquarist-found-dead/
Using a stand alone GFCI protected power bar, along with a grounding probe, is not only a very safe way to protect ones fish, themselves, and family members, but also removes any issues with older homes that have older panels. They also have built in test buttons to ensure that they are working properly, which should be checked on a regular basis, just like all GFCI protected receptacles.
Last year when Marineland Stealth heaters were cracking, blowing up, and basically failing left right & center, my probe/power bar combo picked up stray current from an older Stealth heater in one of my tanks that had begun to crack near the top of the heater, and due to the ground probe tripped the GCI breaker, instead of me having to become the ground on my next water change.
I would have never noticed this in my tank with the naked eye, and it potentially saved me from a disaster as many of these "cracks" ended up with the heater blowing up like a small pipe bomb. In a few cases they actually blew out the end of a few individuals tanks.
The online articles that poo-poo the use of ground probes do so only as stand alone safety devices. Add a GFCI receptacle into the equation and their argument no longer holds water. (no pun intended)