Common grace?

So, I was working in a coffee shop tonight, and there was an acoustic band that was setting up, and I thought to myself, "Self, this isn't going to be good. You came here to work, and you're not going to be able to concentrate."

I'm sure glad that I stayed anyway, because I thought the band was spectacular! Two girls, keyboard, acoustic guitar, beautiful voices. I bought their CD, and told them both how wonderfully they played.

As I was going home, I thought again to myself, "Self, those girls have truly been given a wonderful gift. Praise God for that!"

But then I started thinking about the mystery of common grace. Now, I don't want to assume that these girls aren't Christians, because I don't know that. But I do know that there are many people out there who have great talents, but do not recognize where those talents have come from. People always say, "You have such a gift!" But a gift requires not only a recipient to receive the gift, but also a benefactor to give the gift. For those who do not believe in God, or at least some concept of a god, where do they think these "gifts" come from?

Does something like musical talent fall under the category of common grace? Is the goal of God's giving of this gift to glorify Himself, even through those who do not directly give Him glory? Were these gifts purchased at the Cross, as was saving grace? If so, then how and why are they distributed to those who are not His adopted sons and daughters? If not, then where do they come from, and why are they given?

Common grace has always been, and continues to be, a very difficult concept for me to grasp.

Thoughts?