With iSproggler, you create a smart playlist on your iPod called "Recently Played" and that's what the program checks when you plug your iPod in. Things may have changed, but that's how it worked back then. I had frequent problems though, so I eventually decided to just sync my iPod (to a specific manual playlist, not to my whole library) and use the standard last.fm client. I have occasional problems but I can usually fix things by restarting the app and/or going to help/diagnostics and manually syncing.