I disagree with the "double-action revolver over an empty chamber" statement. When you present the firearm and press the trigger it will go click, if empty chamber carry is done correctly to avoid a negligent discharge, i.e, the empty chamber is rotated in. The empty chamber under the hammer is a different and today completely unnecessary remedy for an accidental discharge of an unsafe revolver that shouldn't be carried anyway.
Hammer down on an empty chamber is a common way to carry a revolver if the person in question is concerned with negligent discharges due something like to a dropped gun. Personally, the only guns I own that are commonly carried in this manner are Colt Single Action Armys or clones of the same. Even then, my Single Action revolvers are range only guns. For more serious situations, I prefer more modern equipment.
My Ruger single actions use a transfer bar system (all Ruger single actions except for the '3 Screw' early model Blackhawk- and even in their case, ruger will convert them for free- use the transfer bar system), so they can be carried with 6 loaded and the hammer down over a live round and none of the actions on any of my DA revolvers make it necessary to have the hammer down on an empty chamber except an antique Smith and Wesson Model 1881 that was built in 1896. Again, that is a range only gun, so carrying it that way would not be an issue- if I'd ever bothered to have leather made for it.
In the case of a revolver, the live round in the chamber adjacent to the empty one does not align with the barrel and hammer until the hammer is cocked or the trigger is pulled. Using this carry method never has made any sense to me unless you are dealing with particular firearm built in the 19th or very early 20th Century that has an action that dictates doing so. I've never bothered with it when carrying either my Smith and Wesson 1917 or my pre-WWII Colt Detective Special. Their actions don't dictate the practice, so I don't do it.
Honestly, I think this practice being so commonly suggested is a case of Hollywood fiction seeping into real life. Cowboys in the movies always carried 5 with the hammer down on an empty chamber and those that don't know any better think that means that's the right way to do it. It is definitely a good idea and the safest way to carry something like a Single Action Army or a 19th Century Smith and Wesson like a Russian or Schofield but doing it with something like a Smith and Wesson Model 10 or even a Hand Ejector is a waste.
EDIT
And I agree completely with you on Condition 3 carry. That's one of the worst ideas I've seen for concealed carry- ranking just below Condition 2 carry of a single action semi auto- but that's a whole different soap box to climb onto.
Condition 3 carry is, in my personal, not so humble opinion, being a gun bearer for a mugger. You've got a gun that won't shoot when you need it. All he's got to do- and he's already got the initiative- is take it from you with your wallet, watch and jewelry. It's not like you can shoot him, the thing's unloaded*.
(*- 'Unloaded' being defined as not in a condition where the gun will fire if all safeties that may be present are disengaged and the trigger is pulled)