I've been using Firewire as audio drives exclusively for about 2.5 years now, without incident. (knock on wood [img]images/icons/smile.gif[/img] .
I started with 3 ClubMac 75G (oxford 911 chips - by sheer luck at the time, had no idea that that was to become a necessity).
I'm now using the OWC Mercury Elite cases exclusively.
http://eshop.macsales.com/Catalog_Pa...=FW&Template=1
Even the 5400rpm 160G's, have been just fine for my purposes (Sound Design, and premix playback of up to 32 tracks at a time). That said, I typically cut with more than 32 tracks activated, withut problems, but I can't say for sure how many tracks reliably play back at once. I've never noticed any limitations, that were any different from the old days of SCSI.
I've been telling people for 2 years now that firewire is great for PT drives, but most still don't believe me, and use firewire for library only, and copy to SCSI for PT playback.