Pure CSS tabs technique

Web maestro Mark Pilgrim is always very generous about documenting his experiments and his solutions. In his Dive into Mark blog he’s working on a new design and has posted a discussion of the \”pure CSS\” technique he’s using to produce navigation tabs.
This is something I’ve been trying to understand for a long time myself. A lot of smart CSS and standards-compliant design gurus have discussed aspects of it online, but not yet in a way that I could fully wrap my head around.
I found one thing Mark wrote oddly reassuring, \”This CSS stuff is hard; don’t let anybody tell you different.\” You can either learn this stuff the hard way, by puzzling it all out yourself, or the easy way, by following Mark’s memex trails.