An interesting look at using consistent line-heights to force a vertical rhythm to a page. Specifically, it looks at setting a base line-height (in this case 18px) and ensuring all text uses it. That means smaller fonts have larger gaps between lines, larger fonts have smaller. I'm not 100% sure I like the outcome on the example page given, but there's definitely some interesting use-cases and applications.

just as regular use of time provides rhythm in music, so regular use of space provides rhythm in typography, and without rhythm the listener, or the reader, becomes disorientated and lost.