A few notes, not too systematic at this point, but rather have them now anyway:
Installation on top of existing MacPorts
This generally works fine, however config files are not overwritten, so it makes sense to review what is there. Alternatively, delete them prior to installation, and new ones will be written.
X11
1. If you plan to use X11/GTK/wxGTK apps, remove any alternative installation of X11/XQuarts from system prefix. It is a few seconds procedure, nothing needed to clean up manually. See:
https://www.xquartz.org/FAQs.html
Unless that is done – at least in my experience – no X11 GUI apps will work.
2. There are three relevant ports of X server (which is needed to run X11 GUI): xorg-server-1.18, xorg-server-legacy and xquartz. xorg-server-1.18 is only needed for Tiger. On 10.5+ use either of the latter. xquartz is much newer, but might not work on some configs. All these can be installed in parallel, but only one can be active at any given time.
3. Upon installation/activation of one of those X server ports, reboot is needed. At least on 10.6.x the first launch of X app may freeze – if it happens, just force-quit the app and launch it again. X11 is not the most robust thing, LOL, but if everything is done correctly, it will work. Unless you build ports locally, just keep X server installed and active, and you avoid most of the headache.
Xcode-using apps on 10.6
Since Xcode is not open-source and there is no Xcode 3.2.6 with complete ppc part, using it to build apps on 10.6.8 on powerpc is hit & miss. Something will build, something won’t, and that also may depend on which Xcode components you replace (3.2.6 is defunct as-is). What works far better generally is building those apps on 10.6.8 x86 (either as universal or ppc-only). There are not many apps which rely on Xcode, thankfully, and those are mostly archaic and seldom useful apps. 10.6.8 on x86 with Rosetta can share apps with 10.6.8 on powerpc (no need to build everything twice).
ppc64 on 10.5
Default config sets ppc as build arch and disabled universal builds. This is a sensible default which fits most cases. However, on a G5 you may instead choose to build for ppc64. (Universal builds are largely non-trivial, and it is simpler to assume it is just broken: build one arch at a time.)
To switch to ppc64, edit /opt/local/etc/macports/macports.conf so that build_arch is set to ppc64 (you may also want to set universal_archs to `ppc ppc64`). Some pre-built ports are here:
http://macos-powerpc.org/packages_ppc64
-devel and -legacy ports
Quite a number of ports exist in “normal” and -devel versions. A few also have -legacy subports. Unless you know what you are doing, it is generally safer to avoid -devel versions (unless something of those is installed by default). There are a few exceptions: qt4-mac-devel is fine to use and at least on 10.6 it is, IMO, usually preferable; mplayer-devel can be used normally; isl-devel is used by default by gcc14.
-legacy versions were meant to be used on older systems (which normally includes powerpc ones), however in some cases “normal” versions of ports build and work, which leaves -legacy ones somewhat redundant (for example, mpv).
G5 users on 10.6.8 (or 10.5.8 ppc64)
Consider adding`+G5` in variants.conf inside /opt/local/etc/macports. This will trigger installing optimized versions of gcc and a few other ports (not many, I have added it only for the primary compiler and a few multimedia ports like ffmpeg). This is not required, but presumably can improve performance. Of course, it can also be used manually, as in `sudo port -v install ffmpeg5 +G5`.