In creating a new database for Rails hacking, I accidentally reset the password for my Typo database. After much scrutiny, it was impossible to tell that the problem was caused by Typo no longer being able to log into its database. There was no connection error in any of the logs (that I could find after days of looking).
I only noticed after I tryed to log into the database manally to inspect the tables for damage. So, not only did Typo not generate an error, but it kept serving cached pages without comment.
Dear Typo: Work or don't work. Half working is worse than broken.