Could anyone explain what the difference is between a shim and a shiv?

It's really a shim; I suppose they may have called it a shiv (prison slang for "improvised knife") to be able to talk about putting a shiv into IE...

Nice book plug. I'm reminded of the old CSS Box Model hack for earlier versions of IE.

For those not already familiar, Paul is the maintainer of HTML5 Boilerplate: http://html5boilerplate.com/

Not directly related, but play around with Paul's site. Lots of little hidden goodies there.