Ever wanted to scrobble to your beloved Last.fm profile those songs you listen on Youtube!?
Now you can :)
First you should have Firefox and then install the Greasemonkey add-on into it.
Afterwards this script.
Almost done! Now in youtube you'll have a new button like this:
Now you should login into your Last.FM account and correct the Artist's name of Song Title if needed... and Voilà!!
Hope that helps.
SergiOL
