I also pick up accents and dialects without trying. I have to fight the urge to say "ya'll" with a drawl when talking to a Southerner, or sounding like Madonna when talking to the British with their "car parks" and "loos" and "tellies." I don't try to mimic them; it just happens. I try not to let it, for fear of sounding like I'm mocking the other person.
I don't know about the accent thing, but I think I've found a scientific reason for my extreme abilities as an empath: mirror neurons. These interesting creatures are thought to be at the root of human empathy and altruism. An article on Salon explains them this way:
Unlike other kinds of brain cells, such as motor neurons, which control muscles, mirror neurons fire both when a person is in action, and when he or she observes someone else engaged in the same action. Before the discovery of mirror neurons, cognitive scientists assumed that we gained access to the feelings of others by theorizing about them. Now we know that a direct experience is responsible for much of what we thought was computation, speculation, memory or inference.
There is speculation that autism may result from a breakdown or suppression of the mirror system, since people with autism are less empathic and have trouble reading the emotions of those around them. Functional MRIs show they have less mirror neuron activity, as well.
I'm wondering if I'm on the other end of the scale. Could my ability to pick up emotions like my bluetooth headset transmits my cellphone calls be a result of having highly active or an overabundance of mirror neurons?
I don't need a scientific explanation to know that I'm attuned to other people's moods. Whatever science proves, I know what is true about myself. Nonetheless, it's always interesting to connect the dots between the mind and the body.