My home music-playing setup consists of a Linux box running MPD, a client-server music playing system. To this, the mpdscribble client is attached, monitoring its status and sending the details of tracks played to last.fm. As of a few days ago, though, mpdscribble stopped working; it connects to last.fm's servers well enough, though once the time comes to send a track, it reports an authentication error, as if the password were incorrect.
I have tried the same username and password combination for logging into the website, and for using the official OSX last.fm client, and it works. I have also tried two other, independent, MPD/last.fm clients (scmpc and lastfmsubmitd), and found that they had the same problem; as, indeed, does the (somewhat old) third-party iScrobbler client for OSX. (This was, needless to say, on two different machines.)
Could last.fm have broken an older version of the AudioScrobbler protocol used by a lot of open-source software? (It appears that these clients use protocol 1.1, whereas there is now a 1.2 protocol.) Oddly enough, a Google search fails to reveal anybody else reporting this problem.