I have noticed that I get a significant performance drop on a Mac Pro with more than 5 daisy chained firewire 800 drives. Task switching grinds to a halt, and the machine often beachballs between applications and takes longer to shift focus. Removing all of the drives from the chain makes the problems vanish. I've experimented with moving some of them over to the usb bus instead, which seems to help, but is thus far inconclusive.
Are there any published guidelines for performance drops with multiple chained drives? I haven't been able to find any.