.bashrc に書いておくと、コマンドの終了までに10秒以上かかったら growl で通知してくれるよ。

beep_if_long_time_past

beep_if_long_time_past() {
    LAST_COMMAND_DURATION=$(($(date +%s) - ${LAST_COMMAND_TIME}))
    LAST_COMMAND=${BASH_COMMAND}
    [[ ${LAST_COMMAND_DURATION} -gt 10 ]] && { growlnotify -a Terminal -t "job finished" -m "${LAST_COMMAND_DURATION} seconds for ${LAST_COMMAND}!"; }
    export LAST_COMMAND_TIME=
}

export PROMPT_COMMAND=beep_if_long_time_past
trap '[ -z ${LAST_COMMAND_TIME} ] && export LAST_COMMAND_TIME=$(date +%s)' DEBUG