emerge is the interface to Gentoo's package management system. I'm having Lightnin' download, compile, and install new versions of everything while I'm off doing other stuff. It's cool. It just takes a really freakin' long time, especially on Lightnin'...600 MHz of pure power!
You can type "emerge world" and bam, it checks for new versions of everything you've got on your system, upgrades everything, takes care of the entire dependency tree, and automatically gets rid of the old packages for you. It's why I use Gentoo.