I'm experiencing the same thing, however, it's more than that. I usually leave my firewire drive on, and the system will get stuck when 10.1 starts up as it checks hard drives. Booting back into 10.0.4 fixes the problem. I tried copying all the FireWire related Extensions (in /System/Library/Extensions) from a 10.0.4 installation into my new 10.1 installation - that at least allowed me to boot up properly, but drives fail to mount. I went ahead and copied and replace all Extensions, and get a kernel panic after that. There's got to be some bug in Apple's new Firewire mass storage or hard drive drivers.