Two more thoughts:
One, I no longer encourage my clients to count calories simply because everyone sucks at it. A recent study showed ten REGISTERED DIETICIANS underestimated their daily intake to the tune of 223 calories.
Two, your metabolism slows for THREE reasons as you lose weight. (1) obviously because you're getting smaller (2) it becomes more efficient and (3) perhaps surprisingly, people tend to burn fewer calories via non-exercise related activity in the latter stages of weight loss.
(2) and (3) could be part-and-parcel of a sort of survival mechanism. In any case, a pedometer will insure the requisite non-exercise related energy expenditure.