I just got bit hard by a MySQL replication error, so I'm about to write a Hobbit client-side ext script that will check the local servers slave status (CHECK SLAVE STATUS \G), parse the output, and alert appropriately (red if Slave Running = No, or if Seconds Behind Master >300, yellow if Seconds Behind Master <300 but > 60...otherwise green).
If anyone already has a script that does this, please let me know, and let's put it on The Shire. If nobody else has one, I will whip one up and share it.
-Charles