Why is Leopard install asking for a reformat to GUID?

[Zoidberg]

What BGnR said. This came up during a firmware update last year (September). You'll be able to boot from an APM drive but you'll get hosed down the road if a firmware update comes your way.

I got around it by booting from my SuperDuper clone, reformatting my internal MBP drive, and then cloning back. Then ran the firmware updater afterwards with no problems.

A few threads from over @ Apple discussion re/the subject. Note that, at the time of posting, I wasn't (apparently) aware of the non-issue with booting from APM as a general rule.

http://discussions.apple.com/thread.jspa...ID=5457590�
http://discussions.apple.com/thread.jspa...ID=5457510�