Sadie does this! I always have scratches and bruises on my legs. She does it to my back in the mornings to wake me up (usually between 6:45 and 7:15, but occasionally earlier, like today at 6:00).
If it's not first thing in the morning, she's usually doing it to get my attention to go outside. For a while, I had her down to only doing it to go out to potty and to wake me up (can't really stop it if I'm asleep). Lately, she's started doing it a little more frequently.
Riley used to paw the air, after watching Sadie. Pretty soon, he got that he was supposed to hit you, but I nipped that in the bud by telling him, "Give me paw," everytime he did it. So he'd hand me his paw instead of hitting me. Now he usually paws at the air, but occasionally, he'll just take a swipe at me, especially at my face if I'm sitting... ouch!