What exactly is MacPorts and how do you use it?
 

My main reason for wanting to know is the discovery that by using the "Gimp.app" package of the GIMP, I'm stuck with GIMP 2.2.11, but with MacPorts I can use the brand new 2.4 release. The problem is that I can't find a satisfactory explanation of what MacPorts does exactly, not even on the MacPorts homepage. Can someone help me out, here?

Thanks.

Did you try looking at the MacPorts entry in Wikipedia?

MacPorts is a program that allows you to install various *nix programs onto a Mac directly, without having to compile everything from scratch. MacPorts also draws in any dependencies automatically. It's essentially a *nix package manager for Macs. There is a similar program called Fink which is based on Debian tools (dpkg and apt). I think that MacPorts (which used to be called DarwinPorts) is based on BSD, but don't hold me to that. I'm using both MacPorts and Fink on a Mac I have at work, and they both work quite well. You have to install the Mac "Developer tools" and X11 first (you can get those from your Mac install discs or on the Apple website, I think). Then you install the MacPorts or Fink program just as you would install any Mac program (they provide .dmg files). After that you can use a shell to access MacPorts or Fink - or they provide gui wrappers too, though I haven't tried those. If you are stuck on a Mac with OSX - as I am at work - but you are more comfortable with *nix programs - especially cli programs, MacPorts or Fink is great.

Check these links for more: MacPorts wiki
MacPorts @ Wikipedia
Fink homepage
Fink @ Wikipedia

Thanks. I actually looked at the MacPorts wikipedia page and was still a little confused, but I think the Fink homepage explains it pretty well.

Macports is great. I got irssi & links through it without any problems, haven't really thought about getting anything else since after installing Developer tools on Mac you already get your standard Unix apps and then some very cool stuff like PPCExplain.
However, O'Reillys "UNIX in a nutshell" (awesome book, if you don't have it, shame on you) tells differencies between OS X, Solaris & Linux apps and to make OS X's CLI tools more Linux-like you could replace some BSD-tools with GNU-versions, if you'd like to. Originals remain intact so it's completely safe. :)