WTF has a scary story about a really bad (and dangerous, and expensive) production failure. My worst? Probably doing an SQL import with some bad characters which resulted in the update of an entire site of content being replaced with one page (ie: something like update pages set content = 'xxx' where id = x;, except that somewhere in the 'xxx' there was a ";" which caused the entire site to be updated). A database restore lost a days worth of design work from the other person working on the project. Luckily a) the site wasn't in production yet and b) the designer had all the pages he had worked on saved and on his desktop so he just needed to cut/paste his work back in.

I too sleep soundly knowing my code doesn't control pouring giant vats of molten metal :)