Well, I know all that time in the womb together had to have some sort of effect, other than physiological. Most twins play very well off one another's emotion. This can lead to, with proper training of course, a strong bond. Some call it telepathy.. I call it empathy.
Twin telepathy is a very curious subject. Seeing as though being born the same time as the other would undoubtedly bring some like minded thought processes and intonement with your twin. I believe empathy would be rather easy to achieve with your "other half". I personally think that it could also lead to some very promising capabilities if handled with the correct expertise.