I have a plastic cake server with a serrated edge on one side. It came with a decorated cake from Albertsons, and it doesn't tear up the decorations when you cut through them. Very handy item. I don't recall how I got it because I've never bought a decorated cake from Albertsons!
Lisa may be right about whacking not working so well on loose heads of lettuce. It doesn't work well on butter lettuce, although it usually does fine on firm heads of iceberg (I actually prefer looser heads, which may be why it didn't always work for me).