My girlfriends dog used to sleep with us. He's about 70lb...and I was noticing I was waking up with about 18" of bed. That was the end of him sleeping through the night, on the bed. Now, I get up before her. He waits for me to get up and the second I leave the room, he's in bed, on my side of the bed.
I was fine with it, until Heather thought it was funny he slept with his butt on my pillow. I thought she was joking, until I caught him one day. Numerous times later, I gave up and stopped yelling at him...until I found a poo stain, on my pillow, one day. That was the end of that.
If we're drunk, or just being lazy, we'll call him up into the bed until we turn the tv off and then he's kicked out.
The new cat, that we got a few months ago, sleeps in bed between us. We've rolled over, on top of her a few times and a few times, I thought she was hurt but she wasn't. When you try to move her, she goes into attack mode and tears you up. I let it slide, mostly, but she's gotten me so a bad, a few times, I've flung her off the bed. I wake up the next morning and she's back in the exact same spot.