I've been doing the 1200 calorie diet. It was hard at first - I started off at 1400-1500 and then tapered it down to 1200, with light exercise (3-4x a week), and when i say light, i mean 30 minutes on the elliptical and then rushing home right after. Eating healthier definitely made a big difference. I avoid calorie dense foods and try to get as much fiber as I can. a typical day is a whole wheat english muffin with boca patty for breakfast, powerbar triplethreat for snack, a lean cuisine and side salad for lunch, designer whey protein shake with low carb soy milk for snack, an omelet or low carb tortilla pizza for dinner, and maybe 100 calorie popcorn after dinner.
I learned how to shop smarter and buy low-calorie versions of things that I like (La Tortilla Factory tortillas, fat free cheese, lean cuisines to cure my mexican and italian food cravings, eggbeaters, etc). If I can't count the calories on something, then I won't eat it. that means steering clear of my boyfriend's mom's home cooking and restaurant food.
I highly recommend using the FITDAY software program. It is MUCH better than the website. That program was my secret weapon =)