Me.
A clients website had been working for the last 18 months. No problems, no code changes, a few software upgrades but nothing big, and nothing that broke the site. Until today. When it stopped working..
Nightmare. What on earth could have gone wrong? The data in the database looks fine. The code hasn't been altered. The log files don't show any hacking attempts. What the hell?
Eventually I do a SQL dump of the database to run it locally. Lo and behold what do I see? Lots of '\r's in the data! Where did they come from? Wherever.. it meant my code that compared a string (part of a postcode) with the text in the database was never going to return true.
Moral of the story: trim() things going into the database if you're to compare them with user input later.
Must have written the original code on a Monday.