I was just checking out the latest build (r16819) on a 5th generation iPod. Actions which require spinning up the HD take around 4 seconds on the iPod and 2 seconds on my Archos V2 Jukebox Recorder. It's a very noticeable difference which has sometimes made me repeat a keypress because I thought nothing was happening. In the file browser there is no feedback (like "Loading") after a keypress and multiple presses get queued and acted upon.
It seems to me that seeks are slower too, and they certainly sound lower-pitched and slower. Who would have thought that an iPod would be a downgrade in some ways.