We had a bookcase style headboard in the past and the pillows would slide up into the open section of the headboard during sex and I hated it. We now have a traditional flat wood headboard that I love, not to mention its more comfortable to prop up against.
I made my own by accident - I pushed my bed against a storage chest, then placed a board over the chest, then it acquired a desk hutch. So now I technically have a bookcase headboard. Since the board is even with the mattress top, I know what you mean about the shifting of pillows (although C and I haven't had opportunity with having sex in my bed).
No headboard, just a platform.
We just bought a king size bed and I am looking for the right 4 poster/canopy set to go with it. Something dark and midieva looking.
Nice thing about the platform-it does not move.