If you're not following Dear Editor you really should be. She takes all sorts of writing questions and answers them on her blog. Today she's got a great post on Character Arcs. I won't post everything she said, because you should check out her site yourself, but this really stuck out to me. About your MC:
"When he reaches The End, extract him from that last scene and drop him back onto Page 1. He should handle himself so well that you wouldn’t even have a story if this were the guy to really start it."
I thought this was a really great way of putting it. I'd never thought of it quite that way. But I can see this is an easy quick check to see if you've created growth in your character. Not the be-all end-all by any means, because of course every story is different and some characters might change in a way that still doesn't allow them to easily handle the problem, but you can still determine whether or not they would handle the situation differently. Because your character needs to have picked up some new skill, or way of thinking, or understanding that would allow them to take a different approach to the same problem.
I'm going to use this line of thought from now on when plotting. What about you, what do you do to ensure your character is growing an changing? Do you have a trick? Do you plot or outline or whatever you do with the character arc in mind?