I've been using My Fitness Pal for about a month. Most of the recommendations that I have read say to enter your activity level as sedentary or light activity to get your baseline calories and then log the specific exercise you do on the days you do it. It will then give you back those calories you burn to eat as fuel for your activity. For example, my daily calorie goal is 1250 at light activity. I biked an hour and 45 minutes today at 15.6 mph which gave me an additional 1,000 or so calories I could eat. It recommends eating all of them to continue at a pound a week weight loss, although not everyone does. (Nancy Clark says to eat back 80%, I think).

I wouldn't worry about the extra half pound. When you get to your goal weight you need to go back in and change your settings to indicate that you no longer want to lose weight but maintain. You will then get a different calorie goal should you want to continue with MFP.

I have found it very helpful, and the data base is the best I've seen.