The MA has directly saved my life a few times. It's also saved me from some injuries along the way.
But, in my estimation, the greatest thing it's done for me was to enable me to pique the interest of the woman who is now my wife. Starting in MA at 8, I think it really helped my overall maturity. So that, at 23, I was able to attract the attention of a 38 year old woman.
When she first met me, she thought I was in my early 30s. If I had had the maturity level of an average 23 year old, she wouldn't have noticed me, much less taken an interest in me. In my opinion, she is the best woman in the world for me and we're a very well-matched couple (been together for 8 years now, married for 6, and never had an argument - when we disagree on something, it's trivial so we either make a compromise or agree to disagree).
So I think that's the greatest thing the martial arts have done in my life.
The second greatest thing, is, as TallAdam said, it has given me the opportunity to meet a lot of good people. Most of my "extended family" (i.e.: friends that are close enough that I consider them part of my family) are martial artists.
Mike