Agree. I've got a Garmin Edge 705 on my road bike, along with a PowerTap power meter. The rule of thumb I've always heard is that 1KJ of work registered by the power meter is equivalent to 1 "calorie" burned assuming a "typical" 25% efficiency for the human body. My Garmin's calorie estimates are typically 1.9-2.0X higher than the number of KJ reported by the PT...

For my tour down the Pacific Coast, the Garmin's estimates of calories burned ranged from a low of 3000 (~55 flat miles) to a high of 5500 (~90mi + elevation). Bike, luggage, and water weighed 51lbs and my average speed was around 15mph. For whatever that's worth.