I don't raid, so this isn't so much an issue for me, but for those of you who raid optimally, how do you handle them? Suppose a hit/mastery or hit/haste (depending on which route you like) piece drops. Do you keep two copies and gem them differently? What about expertise? If you have, say 5 shared pieces, do you reforge every time you switch specs? Or do you not share at all?
If it needs separate reforges, enchants, or gems for each spec, then having two copies is the best way to go. (Actually getting a second copy is the tricky part...) Otherwise a single copy works fine...I just tailor my reforges around that fact.