Even though I'm not religious, I use the time of Lent to make changes in my lifestyle. It works really well for me, I guess because it's a short enough period of time that I can live with the changes, even if I don't make them permanent. But it's long enough that habits can be broken.
I originally started doing it to break my habit of buying books. My purchases had gotten so out of control that I was buying books instead of paying bills. When I spent $225 in 6 weeks on books, I knew it was time to change. I stopped for Lent, and broke the habit. Now I just go to bookstores occasionally, not weekly.
This year I'm giving up sugar. I know it makes me feel like dogdoo -- I get fatigued, my blood sugar goes haywire, I get the shakes and my palps increase dramatically. I'm not going the whole "no carbs" route. Just "added sugar" kinda stuff -- cookies, candy, sodas, etc. I have been in such a sugar craving mode for over a year now -- sometimes I'll eat cookies or ice cream for meals. Something needs to be done. So wish me luck as of February 25. Who knows -- maybe I'll drop a few lbs. too!