I got the HRM (Polar F4) just before the New Year and used it yesterday for the first time!
So get this.... I did shoulders and ab work and then my 3.6 mile run.
I burned 743 CALORIES! The treadmill said I had burned 314 and the monitor had me at over 500 just on the run.
The on-line calculators said I'd burn 50 calories weight training when I burned slightly more than 200.
I'm so glad I dropped the $80 into this. I knew the on-line calculators could never know what I burn if they have no idea of my intensity. And what does it mean when it says "weight training, intense" or "running, moderate speed". How can they really KNOW?
I found it so inspiring that I created a spreadsheet that covers all of it... nutrition, exercise, mileage, you name it, and it's easy for me to fill in and I see the whole thing in ONE spot. It even calculates the deficits so that I know what the scale SHOULD say. (I'm an Excel nerd... couldn't resist!)
So if you are counting calories and exercising and figure out why you're not shedding the fat, I'd recommend using an HRM that calculates calories. Nothing more motivating than having the number right in front of you!