My impression is that most people seem to use Fink to keep their non-core open-source software up-to-date. It’s inspired by Debian’s packaging system, which I’ve never used so I have neither love nor hate for it. Lots of people who hate RPMs like Debian’s packaging system, but even though I dislike RPMs that’s not a good reason to choose it. (Applicability of “the enemy of my enemy is my friend”, and all that…)
But there's also DarwinPorts which is supposedly like the BSD ports system. My server and current desktop both use Gentoo which has its own ports-like system called Portage. I like Portage a lot, and I like the fact that you compile packages as you go. The only (very minor) problem I've had with Portage was when I was for some reason using unstable x86 packages.
So I'm wondering which is the better system to use. Or maybe it's just a matter of playing around with both and seeing what works? I'm already going to have to learn a lot with OSX and it would be nice to have something stable underfoot.