If we're serious about universal binaries, the mozilla project's unify script is useful. Install once for ppc to a given path, install a second time for i386 to a different path, then call unify, telling it where your ppc and i386 builds are, and it combines them into a new third tree, using lipo on any files as needed.
If you can build without using lipo, great, but if you need lipo, then unify is a time saver, not having to engineer all that logic again of figuring out what needs to be lipo'd.
Now it's just a question of licensing, and I'm no expert in that. Is it possible to take the unify script from mozilla and incorporate it nicely into MacPorts? Are our respective licenses compatible for that kind of inclusion?