I don't think it's too common among my friends, either. In fact, I remember a hung-over guildie logging in one morning, shocked to discover that in a drunken rage the night before, he'd deleted his alchemist. I think that moment in time made me covet my characters; I'm almost afraid to delete them even if I never play them, lest I change my mind later. In City of Heroes, for example, I frequently moved abandoned characters to remote servers just in case.
But other folks delete to dramatize roleplay, to get attention, to ensure they can't return, or to ensure a clean slate if they ever do return. What about you guys -- have you ever killed off or deleted a "serious" MMO character? And can I have your stuff?