1) It's not gonna be called the G5, as the whole 'G' thing is "generation" (of PowerPC), and that name is joint-trademarked by Apple, Motorolla (as well as the new Freescale) and IBM
2) I'm guessing they'll keep the same case-design for a few years, the same way they kept with the candy-ish plastic over multiple generations
2) I'm guessing they'll keep the same case-design for a few years, the same way they kept with the candy-ish plastic over multiple generations