There is a bash script to build a Mac OS X .app bundle from an application written in Go that works by extracting the necessary libraries, resources, etc. from a Homebrew installation and tweaking the libraries. I'm happy adding MacPorts support, but..
Aren't there easier ways to do this, like using Xcode projects or whatever? Is there an analog of py2app for go? What should I know about using outside libraries in .app bundles?
If I understood you properly, you want to pack a Go binary as a OS X .app file. Well, yes, you can do it. Take a look on Makefile of my cocoa-go project. In fact, building .app if fairly easy. Also, I can recommend a Developer Library article about bundles — Bundle Programming Guide.