I feel that unless this is an application-level question like "How do I blur this image in PhotoShop", all questions about MacOS are fair game.
We should not limit ourselves to the "Unix core", because depending on your brand and style of Unix, that can be a pretty lonely subset.
- Stripped down Unixes (Busy box for example)
- Full server environments like Red Hat Linux Enterprise, MacOSX Server, SUSE Linux
- X11-powered desktop environments, the most common (Ubuntu, RH, Fedora, OpenSUSE)
- Android-powered desktop environments, like aPad, ePad
- Android-powered mobile environments, like the NexusOne
- MeeGo-powered phones using the Qt stack
- MeeGo-powered netbooks using the Clutter stack
- MacOS X, with a UI powered by the Cocoa/Quartz stack
- iOS/iPhoneOS, with a UI powered by UIKit/Quartz
- Consumer electronics, powered by DirectFB, barebones X or other lightweight windowing system.
I do not believe we need a StackExchange for each of those, instead we should introduce tags for the specific domain of the question, like "x11", "quartz", "ios", "meego", "desktop", "server", "macos", "busybox", "bsd" and even have distribution or brand specific tags like "freebsd", "openbsd", "redhat", "fedora", "ubuntu" and so on.