Earth (isolated) ground vs. wall outlet ground.

If you have hum in your system it probably is a ground issue. You should consult a licensed electrician. Multiple ground points can create voltage differential... bad. There are options if you are having noise problems, which often show up in older installations where multiple neutrals are tied together for expediency. Electricians are familiar with grounding problems, they can play havoc with computers. Maybe not so familiar with audiophile equipment, but many of the same issues. The ground stud is there for your convenience, Some of the older 2 wire components ground through the shield of the interconnect. When that is not sufficient, or an incomplete circuit, the ground stud, or a cover screw, can be of use. Most equipment in the phono side benefits from a physical ground, BTW, if you have hum from an older 2 wire turntable, turn the plug 180 in the outlet, realigning the neutral. Be careful, you can do worse than hurt yourself (or someone else). Consult a pro, and don't mess with the panel.

Great answers thanks. But what of the grounding posts on much equipment, including grounding blocks and common grounding of equipment I have seen mentioned? Are these only for systems with poor electrical grounding?

The electrical ground that comes from the service panel is for safety. Millivolts of difference in a ground potential won’t affect the safety features.

The problem with a lot of audio equipment is it ends up with multiple "ground" references, with some or no relationship to the outlet, and the transformer center taps fighting to be "correct."

The worst such problems often come from PC’s which have a very different "ground" for the electrical interconnects than the power plug. This is why proper grounding may become an issue. It has nothing to do with the quality of the wiring in the home, and yet, the quality of the ground in your home is important for life safety.

IMHO, the best configuration for high quality audio is to float the signals with no relationship to the earth/safety ground. My Luxman integrated does not use the AC ground at all. This is probably breaking US/UL regulations but as a result what I do not have is a ground loop. :D

You may notice some DAC makers make a point of touting the incoming copper connectors (USB and coax) are galvanically isolated.  Sadly, not all DACs do this.

Puritan Audio offers a product Ground Master that requires adding a seperate ground rod that connects direct to the Puritian PSM156 power conditioner. They say it is safe, any thoughts?

@yesiam_a_pirate Let me reflect on my radio broadcast engineering days: If our studios (and offices) were co-located at a transmitter site, with a broadcast tower (i.e., a giant lightning rod in the sky) on the property; we mainly grounded audio equipment and broadcast equipment to reduce or eliminate lightning damage. 99% of the time this also helped in reducing hum when connecting numerous studios full of audio equipment together with each other. Many times broadcast audio equipment also had *this* grounding lug on the rear chasis panel. Now if you had a professionally built broadcast facility; you typically had a 3" copper ground strap running between all studios; which terminated at the broadcast tower's ground system (or if you didn't have a co-located transmitter or tower, the ground was tied to the building's star ground system). When that 3" ground strap was available, each equipment chasis ground lug was tied to this ground strap (along with plugging the 3 prong AC plug in the wall for power). If lightning struck the tower, this ground strap provided an extremely low impedance ground, but more importantly it kept all equipment connected to it at the same low impedance ground potential. I still employ much of what I learned and used at broadcast facilities on my home audio and grounding system. The result is extremely low noise floors. 

To lift or not lift the pin 1 connection on an analog XLR connector is another topic related to grounding. In a broadcast facility it's almost impossible to control this issue with sometimes hundreds of XLR connections taking place (in the good ol' analog days), but since most radio stations had decent star ground systems incorporated, this most times wasn't a problem. Now almost all radio stations are wired digitally, eliminating a lot of ground loop problems. Again, this same scheme can be incorporated into home audio systems with numerous pieces of balanced analog gear interconnected. IMO it's much easier to control this in a home environment as compared to a radio station environment. Learning how to solder can be a very important skill to know when setting up a home audio system, as you'll want to be able to unsolder or solder, some of these pin 1 XLR connections when hum presents itself.