I think that for most people, the psychological effects of poker are far more negative than they are positive.
Having said that, though, I think that if you approach poker with an open mind, with humility, and with ego firmly suppressed, you will learn a lot about life in general. I think playing poker brings us up against the basic toughness of life; the uncaring nature of the cards (universe), the basic selfish struggle versus other men (basically a pared-down version of our modern economy), and admitting that we are very imperfect people with much to learn.
If you can open yourself to all of these things, and admit that you are basically not even approaching 1% of the way on your lifelong journey of improvement, then poker might actually be good for you psychologically.
It'll probably crush you, though.