I agree that it depends on the baby, but it also depends on the mama!
I am a little overweight, so I didn't feel baby move much at first. Also, when I first started feeling the baby, I only felt it in the front. Just last night a I felt a kick toward the back. The babe may be facing your back, making it harder to feel movement. Plus, if you are up and moving around, you may not notice baby moving like you would if you were sitting or lying down.
I agree that as long as you're feeling some movement, you're probably fine. In a couple weeks you might be posting that the babe is keeping you awake at night because s/he's moving so much! (That happened to me last night--almost 2 hours of jumping, kicking, and rolling!!--not straight through of course, only when I was about to fall asleep!)