Just to let everybody know:
I recently bought an external USB 2.0 high speed multi-format card reader. While my CF and SD cards mounted fine, transfer speed was slooooow. Really slow. Like USB 1.1.
After a lot of testing (and actually buying a 2nd reader) I settled down to reset the PRAM on my G5 and Powerbook 12".
That did it! Transfer speeds jumped. What was minutes before is now seconds.
So in case you have some weird USB issues -> zap it!