I use them. We had a Paladin NPC in the group that was known to always talk to himself. Each time I roleplayed him talking to anyone, I always mentioned how he always had 1 hand gripping the handle of his morningstar as it hung from his side. It was a habit of his.
Then when the group failed to stop Orcus from returning to deity status, he lost his Paladin status due to his cowardliness. Being ashamed of himself, he decided to retire, and he gave the cleric PC (the Paladin was his mentor/leader) his morningstar.
As soon as the PC picked up the morningstar, he heard a voice in his head introduce itself as Dahkut the Giant Bane. That's when the PCs learned that the Paladin wasn't crazy & talking to himself. He was talking to his morningstar. But he can only communicate with it if he is holding it.
Even though the players never heard Dahkut before, I still portrayed the Paladin having a conversation "with himself". It usually involved the two discussing their thoughts about a PC or an NPC they just met. Dahkut likes to give his opinion about situations in an attempt to be helpful. That's how I roleplay him.
The only difficult thing about using stuff like this is that I always forget to roleplay them. If I don't have an NPC sheet infront of me, I forget about it. Maybe I need to create an NPC sheet for the intelligent items and animal companions/familiars.