I have had this issue for years now on all my Macs. It happens to me with my current iMac intel, which has 2 firewire drives connected to it (one 800 and one 400). When the firewire drives randomly spin it, it sometimes makes my iMac stall a bit. Like the beach-ball will sometimes even come up, but otherwise it just like it freezes a split second while it's bringing the hard drive back up the speed. Why does it do that, and is there anyway around it? It makes using an external drive frustrating and hurts the beautiful mac experience. I have 4GB of memory, very fast computer otherwise, so it's not that.