Personally, I think that magic is something everybody has, and most people have one or more areas that they are particularily good at...
For example, I'm always right on with tarot cards, unless I'm reading for myself (I'm vaguely superstitious about reading them for myself, so I don't... Yeah I know, 10 years, and I still balk at that.
), and I'm reasonably good at putting energy where I want it go, as well as being a summoner of sorts (meaning that I enjoy contacting spirits to request help whenever I can... They just seem to like me
). Crazy on the other hand is a healer extrodanaire, and following something similar to a shaman's path, even if she insists that it's completely different... My Grimwell is incredible at manipulating people (small stuff, like making drivers move to a different lane than the one he's in while driving) and let me tell you, nobody I've met is a better "combatist" than him... I mean, The guys taken care of 50 year old toxic spirits on his own!
Of course, it takes years before you tend to figure out what your specialties are.
As for how often it works... I've always considered magic to be something that allows me to stack the odds of getting something I want quickly in my favour. I have cheap rent (in Calgary, I'm paying over $350 less than most people for what I have), a guy who loves me (been together over 10 years now, and he was voted "most likely to die a bachelor' in high school), I have a great job with room for advancement, and I've healed myself and my fiance of a couple of major health problems, so that they don't bother us.
I'd say that magic works wonderfully and often, so long as you believe in it... And as a newbie, I remember that's the hardest part, especially since you need complete trust and confidence in yourself first.
But no fireballs yet... trust me, I'm still waiting for that skill to materialize.