Oh, I've also caused an outage by adding a filtered index. But the system I work with a product and we make clear what we support and not. Turned out the customer had an outdated version of a DLL which connected with the wrong settings.
And any use of the wrong settings for ANSI_NULLS etc is an accident waiting to happen.
You have checked sys.procedures for procedures with bad settings, haven't you?
Erland Sommarskog, SQL Server MVP, www.sommarskog.se