If you want to have one single tag, use macintosh.
If you want to split the questions into two groups, there are several ways Macs can be divided. For example:
Portability
- mac-desktop
Mac Pro, iMac, mini, Xserve, PowerMac, Cube
- mac-laptop
MacBook, MacBook Pro, iBook, PowerBook
Era
- mac-ppc
PowerMac, PowerBook, iBook, Cube, iMac (some)
- mac-intel
Mac Pro, mini, Xserve, MacBook, MacBook Pro, iMac (some)
or
- mac-obsolete
PowerMac, PowerBook, iBook, Cube, PPC-based iMac, 68020, 68030, 68040
- mac-current
Mac Pro, mini, Xserve, MacBook, MacBook Pro, Intel-based iMac
And of course, there are bound to be questions about Linux on devices that ship with iOS (iPhone, iPad, Apple TV), so you might want to keep those in mind, too.