I made my way over to the Wikipedia article on the so-called Man with No Name to read the debate on his being one character or three.
I must say, it's even more terribly written than one would expect from a wiki. The arguments saying he's one character seem incredibly weak compared to the evidence that Sergio Leone and his collaborators did not intend it to be one character and the strong suggestion that he's named seperately in each script. Even that would be fine, except that they're all phrased in such a way as if they'd trumped with their brilliance.
The continuity issues are quite interesting, but most seem merely intriguing, possibly in-jokes.
But the name arguments are incredibly weak. My favorite being the idea that being referred to by a name by only one character somehow in itself invalidates it as a name. Yes, it's not quite intended that literally, but the repeated use of it as "proof" only makes it grow in absurdity, especially since once must conclude that Tuco calls him "Blondie" definitively because of his blonde hair, which I think is arguable at best.
This was a lot of words, however, for something that wasn't my original point in posting, which is that it says, "Joe is used in a similar fashion to Mack - i.e. as a way to address a stranger (cp. the expression 'average Joe' or the popular song 'Hey Joe')". Now, ignoring the maddeningly awkward phrasing - especially since I'm often guilty of similar excesses myself - but I must say it's never occurred to me that the character in the song "Hey Joe" wasn't indeed named Joe, although, I suppose, an argument could be made.
The contrary argument, however, is that "Joe" seems to share an awful lot of intimate details about his life to someone in essence yelling out, "Hey, dude! Where you going with that gun?"