The problem is that trackpads are just too small. If I move my finger fast enough to cause acceleration, I have no control at all over where the bloody thing will end up. So I generally disable or at least drastically tone down acceleration.
If you run with acceleration on, maybe this is useful -- but then as far as I'm concerned the rest of the screen is much harder to reach (don't move your finger too fast! oops, now the mouse pointer is who-knows-where).