The designers of Audioscrobbler have become employed by last.fm, and the two engines are to partially merge. [Source]
Last.fm will be "powered by Audioscrobbler", and will be able to play you recommendations based on what you listen to at home through Audioscrobbler...Audioscrobbler will remain free and open source, as will some of last.fm.
There was a piece about last.fm in Wired News last week, and also an article about the social side of Audioscrobbler in the Boston Globe.