Crash course on the CSS line-height property

A nice slide deck that goes in-depth.

The gist of it is using number values (not percent or em or px) is generally the best all around solution to scaling line-height with differing font sizes proportionally, and it suggests tweaks for issues with this like subscript/superscript and IE 6 inline images.

So... use number values. And if you care why it is best or why workarounds for superscript are necessary, check out the (99 slide!) slide deck.