At the first flutter of movement the baby has, it's hard to tell what you're even feeling. When the baby really gets moving you think, "This is so cool!" because you can imagine it kicking out a tiny elbow, or turning over. The "every once in a while" nature of the movement is so novel and so interesting!
I'm at the point where I'm wondering, what in the world is he/she doing in there?!
A while back I read something that said, "You'll think you're carrying a baby octopus the way it can poke out in all different directions!" I'm not into the whole animorphic thing, but I understand the sentiment now. Moreover I've started imagining what he/she could be doing that requires 18-20 hours a day of constant movement.
Pulling taffy? This activity would reasonably explain the long amount of time he/she likes to stretch all the way out on both sides.
Knitting a sweater? That would explain the elbows that poke out in a fairly consistant rhythm.
Training for the Olympics? Depending on what event it's for, this could work to explain the rolling over at a sometimes alarming rate.
Building a birdhouse? Now I'm just being silly. =)
The one nice thing about the activity? The baby sleeps at night! During the day, forget about it. But at night he/she settles down and I am able to get some (uncomfortable, abdomen-stretched, knees-aching) sound sleep.
Now let's just see if little miss/monsieur wonderful is a night sleeper in the outside world!