[symphonix]

I vaguely remember someone saying you can't boot off a firewire drive *YET* though I'm not sure how reliable this info is.
Frankly, I wouldn't bother. How much of a performance gain do you expect by switching to an external drive? And would it be worth the inconvenience of two separate systems running on your machine? I also assume that once booted from an external drive, you couldn't even think of disconnecting it without shutting down, not verry convenient when you have to pack up and hit the road. And, as you've already worked out, implementing boot-off firewire is a heck of a job.
I just get around the problem by not shutting down! The iBook will sleep for days without mains power, and in 10.1 comes back to life faster than ever. I restart it every week or so just to keep the system tidy. Sure, it boots slowly, but I never have to wait for it to boot - I just pull it out of my bag and open it up.