i-Packages are compressed sets of files and instructions used by i-Installer, the open-source package management utility used by many to install, update and remove gwTeX (the standard LaTeX distribution for OS X) and related programs, such as fondu, ghostscript, etc. It’s a good system, since the files that must be downloaded are very large, and a nontrivial amount of configuration is necessary to get things working correctly.
But something always bothered me about i-Installer: it mostly requires an internet connection for it to work. Obviously you need the connection in order to download the software, but for removal too? What if, when WWIII starts and all of the ISPs go dark, I decide I don’t want LaTeX on my system anymore?
I finally figured out how to work around this annoyance (at least for most i-Packages). Normally when you install an i-Package, a few basic files are installed on your computer, and the rest are left on the server, since they’re not all necessary. This is efficient: you spend less time downloading, and the mirrors spend less time serving up data that you don’t really need. But by opening i-Installer, selecting an i-Directory, then opening the desired i-Package, you can choose to download the entire archive, including the configuration and installation instructions.
To do this, select Make Fat from the i-Package menu:

Then the entire i-Package will be downloaded[*]. If you want to modify the package, even with no internet connection, you can double click on the ii2 file (the i-Package itself) which will open i-Installer and allow you to perform any of the actions for which scripts have been written for that package.
The reason why I think this is important is that, because of their Linux roots, most of the LaTeX-related programs for OS X are installed directly in the BSD subsystem (/usr/local, to be exact), so uninstalling them is most definitely not a matter of dragging the application to the trash.
Anyway, with this new-found knowledge, I have become a born-again gwTeX/TeXShop user[**].
[*] i-Packages are stored in ~/Documents/i-Packages.
[**] As an aside, I have also discovered TeXShell, a frontend for gwTeX and teTeX on OS X that works just like CMacTeX — drag files onto the icon and they are processed by LaTeX (or send them to TeXShell from within TextWrangler using an AppleScript). Very convenient.