I think I'm having the same problem. Macbook Pro, 10.4.8. SuperDuper previously worked well backing up to an external Firewire drive when I was running 10.4.7. Now the backup gets about 60-70% through (according to progress bar) and perhaps more (according to the count of the files analysed), and stalls. My CPU usage goes through the roof and practically locks up my system.
Just wanted to let you know.