Is there a way to measure replication lag in MySQL with a resolution less than 1 second?
Have you tried maatkit heartbeat ? This is the one I'm currently using. You will need another perl process running, but from my perspective, this is much more helpful than the current MySQL mechanism.

I'm also using mk-slave-delay to generate lag. I keep a 1 hour lag in one of the slave to have an extra layer of protection in case of SQL injection or user errors.

These two scripts do the trick.

Saludos