Recent research by Emily Lykin and Ruth Baer at the University of Kentucky (Journal of Cognitive Psychotherapy: An International Quarterly, 2009, vol 23(3)) showed that the long term practice of meditation (over 7 years) has positive effects on psychological well-being. Long term meditators were compared to non-meditators on various tests and they reported better able to
Observe
Be nonjudgemental of their experience
Be nonreactive
Enjoy psychological well-being
Ruminate less
Reflect
Not get carried away by their thoughts
Regulate emotional states
Be more self-compassionate
They also found that being more mindful helped reducing fear of emotional states, rumination and increased behavioural self-regulation.
Ottawa Mindfulness Clinic 
I was not a part of the study but have been meditating a few years and can attest to these very results in my own life. It is refreshing to see that what has been experiencially know to meditators for 1000s of years is finally being validated by contemporary scientific discourse.