[Mac] strikes me as the single most superfluous tag. [OSX] while seemingly useless at a glance, is actually fairly useful for categorizing general system software questions that aren't specific to one version or another. Similarly, [Apple] makes perfect sense as a tag for questions about Apple, The Company, rather than Apple, The Subject - But if folks would rather that tag be [Apple, Inc.], I don't think that's a problem either.
Questions about Mac Hardware, should, for clarity, probably be tagged with the particular product line (i.e. [iMac], [PowerBook], [Mac Mini]), or category ([Notebook], [Desktop]). I can really only count on one hand the sort of questions that could generally be applied to all Macs across that sort of categorization scheme that would actually benefit from a tag of [Mac] and not something else entirely.