This eventcmd script uses sferik's T command-line Twitter client to tweet the now-playing song and artist. I've set it to use the songbookmark trigger, but of course you can use a different one.
# create variables
while read L; do
k="`echo "$L" | cut -d '=' -f 1`"
v="`echo "$L" | cut -d '=' -f 2`"
done < <(grep -e '^\(title\|artist\|album\|stationName\|songStationName\|pRet\|pRetStr\|wRet\|wRetStr\|songDuration\|songPlayed\|rating\|coverArt\|stationCount\|station[0-9]*\)=' /dev/stdin) # don't overwrite $1...
case "$1" in
echo '#NowPlaying: '$title' - '$artist' (via #pianobar)' | xargs -0 t update
|> "I Want You To" by "Jem" on "Down To Earth"
[?] Bookmark [s]ong or [a]rtist? s
(i) Bookmarking song... Ok.
Tweet posted by @smartwatermelon.
Run `t delete status 302505518990229504` to delete.
I guess this would be something for the wiki (which does not exist yet).
I was hoping it could be added to the eventcmd samples.