I've seen them done well on several projects, and I've come to believe there is no "right".  As I mentioned above, the first relationship of People over Processes means that if the people are happy with what is going on, that's good.

For the common practices, the biggest difference I've seen is the difference between the chickens and the pigs.  The daily standups are for pigs, not chickens. The backlog is for anybody to fight over, but the active sprint board is for pigs only, and each pig can only post or move their own bacon. 

The biggest failure I've repeatedly seen is violation of the Sprint commitment. This is doubly-true when people other than the 100%-committed developers add anything to the sprint. It doesn't matter how important that bug or new feature is, that was not part of the sprint commitment. If something absolutely must be added, they give it to the Pigs (the developers) with a stated priority.  The developers then re-evaluate the commitment, and the developer who accepts the task must remove an item of similar size in order to accept the one coming in. Far too often when it goes bad, it is because every bug and design request gets added to the running sprint, violating the nature of the commitment.  If the specific developer did not commit to doing it up front, or did not account for the time in their plans for the cycle, then it doesn't belong on the board.