qtscrob (http://qtscrob.sourceforge.net/) can submit tracks that have been
played on your iPod, MTP, or rockbox device to last.fm. Since the Amarok 2
series is focusing on internet service and last.fm integration I think this
would be a great feature to implement.

As you can see from the link, qtscrob is GPL so it may even be possible to
re-use the code.

A simple right click --> sync with last.fm option on the player's library would probably be a good way to do it. An option to sync automatically might be appropriate as well.

Edit: foobar2000 (with plugins) and the last.fm client also implement this functionailty with iPods, but since qtscrob is open I thought it was the more useful link.

Also, I went ahead and filed a wishlist bug.

edit2: And apparently I fail at searching, as it's a duplicate: https://bugs.kde.org/show_bug.cgi?id=183145