I lost 35+ lbs using fitday.com and a polar heart-rate monitor w/calories burned function.

A couple of things I did with that though:
I put in a higher-than-actual weight into fitday to calculate my "normal" calories burned per day (BMR) by about 5 lbs.
For activities in fitday, I always selected a lower intensity workout. So if I did a 15-16mph two hour ride, I would enter a 13-14mph two hour ride.
All calorie readings from the polar HRM were reduced by about 10%.

It took a couple of weeks to get things right, but then I lost 4 to 6 lbs a month for 7 months straight. Was this perfectly scientific? No. Did it work? Absolutley.

For counting calorie intake, I was fastidious about everything down to the teaspoon of sugar in my coffee to eating a handful of grapes. Use measuring cups and a scale when making your meals.

Check out the Nutrtion forum on BF for lots of good ideas and info.