First thing that came to mind was Seidenberg on the 2011 team. The man was +3 on a +55 team where the only better defender on the team was +33.
What is that +3 telling me? Zero.
I'm sure we could get into this pretty nicely, maybe to the point where I learn something. But my first instinct is the +/- tells me far less about a player than the fact his coach plays him fewer minutes regardless of his relatively good +/-. Might be a coach thing, might be the team has better metrics than +/- to base effectiveness on or it might be +/- is identifying an underutilized player. But while I have nothing on hand, I am pretty sure more than one person has done an R² regression to see if there is anything that correlates stronger with +/- than the relative strength of the team.