I don't believe in them. In my personal opinion, they are the perfect opportunity for people to idealistically theorize their life in a new and changed way, but usually the work involved in that new life is one that is daunting and, surprise surprise, is work that never actually gets done.
Take for example, the classic resolution of working out/getting healthy/getting in shape. Oh it sounds good, it really does. You hang your bikini up on your refrigerator. You place a picture of your "fat" self on the mirror and every morning stare at it in hopes you will lose the last 25 pounds you've gained by being lazy. Hell you'll even hit the gym a few times that first week, all excited and ready to sweat off those unwanted love handles.
And then it hits you like a ton of bricks. You're sore. You're tired. You're hungry. Salads taste like rabbit food. The pounds don't miraculously fall off. WTF.
Now folks, this is where it counts. This is where you have to dig deep and actually JUST DO IT. I know, I know, classic Nike cliche but seriously. Keep going. Don't give up. You WILL see results. Just get your little (or big) a** to that gym. If you want some really great inspiration I recommend this blog http://slowmiles.wordpress.com/ to get your butt moving...
My motto: The harder you work, the harder you get to play.