I think if someone was hearing God, then God being at least a metaphor for the Highest principal, the person concerned would act in a very informed and intelligent way. If this were the case that individual would/may inspire people around him/her to act via these same principals. This in my eyes would be no bad thing.
If on the other hand the person is imagining God talking to them, given that they are in a mentally confused state to think God is talking to them in the first place, I think probably their actions would be quite different.
Jesus never quoted from the new testament(obviously it didn't exist at that point), he was an independent.(that's if you believe Jesus existed at all)
I think that people who say they are talking to God but only quote from the bible are in my eyes dubious.