Log Current Delay

I would like pt-slave-delay to log the current Seconds_Behind_Master to the log file or to a separate file. This would assist in monitoring the replication delay without having to start up the slave's sql thread to find the current delay.

Ideally I think the most flexible option would be to specify a file in the same manner as a PID file that would contain just the most recent 'Seconds_Behind_Master'. Another option would be to log the delay in the log:

2012-07-25T21:03:40 Reconnected to slave
2012-07-25T21:03:40 Current delay: #####
2012-07-25T21:03:40 slave stopped at master position mysql01-bin.003898/606237128