TwiTunesというAppleScriptをiTunesに入れておいて、つぶやきたい曲があったらスクリプトを起動してつぶやく、という訳で自動じゃないよー。

ポイントは、このへん：

-- get properties of the playing track
tell application "iTunes"
    set thisTrack to current track
    set trackName to current stream title
    if trackName is not equal to missing value then
        -- playing a stream now; get the name of stream server
        set trackArtist to the name of thisTrack
    else
        set trackName to the name of thisTrack
        set trackArtist to thisTrack's artist
    end if
end tell