Thanks for the replies guys
I can really see where both the variable load reading of the Voltwatch and the constant load of a voltmeter could both be useful. The constant load might give you a better feel for actual battery capacity. It makes sense to me though that if you always checked the Voltwatch under the same conditions (ie. always before flight, or always after flight, or while deflecting one servo, whatever works) that it would give you nearly as consistant a reading as the voltmeter.